I just bought a pontiac 455 for my 1968 firebird.  The car has it original 350 and I'm hoping to slip in the 455.  I read Junker to Thumper.  You know 1976, 455, 210 HP, add headers, intake and cam and you get 351 HP.  Yaa I love what article.  
Any why the 455 is a 1972, 485428 YC code, which I believe has 250 HP, but I discovered the heads on it are 1975 vintage with the 5C code, 7.6  compression ratio.  The heads on my original 350 are code 17 with 8.6 compression.  Should I swap the heads?  obviously I'm an amateur. Any help would be great.

Thanks,
Tom

i agree with Astro. u shud not put small block heads on a big block.  

Okay this head swap might not be advisable, but, correct me if I'm wrong here guys,

My understanding is that there is no "big" and "small" block Pontiac in the sense that there are big and small block Chevys and Fords.  They came with 3.00 or 3.25 inch mains so you can't use a 455 crank to stroke a 350, but the heads should swap.  I'm not saying it would be a good idea in this case, but it's a little different than trying to bolt SBC heads to a BBC block, am I right folks?

BOP men, enlighten us.  What's the best way to raise compression on a smog era Pontiac?  How much can you get by zero decking the block?  Does anyone use domed pistons, I've heard that Pontiacs don't like them. How much milling can the heads take?  Can you have larger valves installed in the 350 heads and port them a little and away you go, or would the expense be such that you might as well get Edelbrocks?  How hard is it to find the better older factory castings?

i think that u are best off by leaving the heads alone. save time, money, and possibly your engine  

Hey thanks for the good advice.  I won't be using the 350 #17 heads.  Another thing I though of, maybe I'm wrong'  the 455 has an increased deck hieght to support the longer strock so would I need to use 455 push rods with the older 400 heads?  Or can I make 350 hp with this thing buy out of this thing with just headers, intake and cam?  

astroracer has given you some pretty sound advice. The mid seventies 6-x heads from 400's are a pretty popular swap and are what I am using on my current street 455 with just a valvegrind. 350 horse from a 455 street engine is pretty  easy. I would suggest buying Jim Hand's book -How To Build Max Performance Pontiac V-8s, from S-A design. the part # for the book is SA78. Pretty much everything you need to know about building a strong street engine is in it. Good luck on your build and congrats, 455s are torque monsters. Edelbrock heads are overkill and really unnecessary unless you are planning on over 500 horse. Try to find a shop that is familiar with Pontiac engines for your machining, you'll get a much better job.  

I have 5Cs on the 455 in my 70 GTO, they work great and have 2.11/1.66 valves. They are from a 400 and not original to the block. All Pontiac blocks (except 301 types) have the same deck height, use the same size rods, same pushrods (excluding RAIV they are thicker but same length) and the same head gasket.

This engine pushed my 4100lb goat to 13.50@105 with a stock 1900 stall converter, TH400, and 2.93 gears, through the mufflers on 87 octane all motor. Considering a 68 Bird should be lighter than my Goat, you could run quite a bit faster with a set of 3.42s in your car. I was running a Performer intake with an 850 Holley but it likes the current 850 Demon and RPM intake better, not to mention the 3.42 gears in the 12 bolt.

There are breaks through out the years such as 65 up intakes being different than 64 and before, also 67 up had 14 degree valve inclination and 2.11 intakes. All 4 barrel heads have factory screw in studs and guide plates.

Flat top pistons are standard on all engine sizes, the factory changed compression ratios by using a different size combustion chamber. FYI a 72cc head on a .005 deck 455 .030+ and a stock type gasket will net around 11.3:1 and even though Pontiacs have fully machined chambers that is too high for a large bore to run on pump gas. Its race gas only time, no matter what you may have read about an engine with 13:1 runnin on pump gas, sure it might for a while. If you do it, have fun with the rod bearings.

ps you chevy types are entertaining with the small block big block thing... even after hearing it for the last 20+ years its still funny

you know guys ive relized someting im a retard with all this motor crap. ive got a 67 cutlass and recently have a 455 pontiac motor a best freind gave me befor e the military and i think by reading your chinese on motor ccs and sbc and all the technical crap i didnt understand ive been trying to get the motor running and i think i may have ruined it. #### .. this thing is a monster and running pump gas and not being able to figure the timing and being new and the p4 intake and not understanding the motor makup and ####, ####. i took the car out and showed my friend how the car was running and how the car would have a like hot knock after warm up and we couldnt figure it out . one day i went with him and couple of freinds for a drive to diagnose the motor and i got pissed and took a slight turn and stomped on the gas . the motor hooked up and the sum *** was like tearing crap up the asphalt was flying and was almost out of control . we came to a stop and all yelled holy #### and realized that this thing was pretty dam impressive. this is in a 67 cutlass which weight was high and full tank and four big guys and it scared the #### out of us all. now ive broken the motor down and realize the bearings are distroyed and terrible and we dont understand what went wrong. the crank is scored but not sure how to go about doing the crank and who to trust. man im so pissed. i could cry.

Oil starvation and over heating usually play a role in ruined main bearings.  

yep nd i think the oil pan being smashed when i placed on cart and not checking the pickup more thoughly it wasnt all way in and i noticed a two and half inch crack in the harmonic balancer. and the top timing gear the bolt was able to be unscrewed with my fingers... hmm wonder what the problems are? lol yea the bearings were toast . but i didnt drive long at all so im hoping the crank will  be able to turn. im really bummed im may have to put my 350 olds motot back in . moneys are tight now.