I have a 66 Fairlane GT with the original 390 in it. I want to keep the original engine stock.i have a friend that has a 391 out  of a bus .ive never heard of a 391.do these engines have any performance potentail or should i keep looking for another 390,iwas also told that a 360 truck engine would work as a replacement for the stock 390 and would use the same parts as the 390 and made better bottom end torque than the 390s. also do u know of any one that makes a efi kit to replace the carb. it would have to be complete because i dont know much about efi systems. i ,d like to get around 400hp out of the new engine so any help would be appreciated.  

I've heard of the 391 but know little about it. As far as the 360 goes, its just a destroked 390 and doesn't have much potential. I'd stick with the 390 or move up to the big inch Fe's.  

Your 390 is an FE motor.  The 391 installed in medium- and heavy-duty trucks is called an FT but it's in the same engine family. FT blocks are cast of high-grade-alloy iron with manganese, silicon and other alloys added to improve durability. Most blocks are strengthened in the crank support areas with much thicker main bearing caps and webs than those in the FE blocks. Also, the FT came with a forged crank while your FE is probably cast, but note that the crankshaft-nose diameter is larger on the forged-steel FT cranks to acommodate a power takeoff. FT noses measure 1.750" compared to 1.375" for FE cranks. Hi-po FE builders have been turning down forged FT cranks for their FE buildups for years.  But remember also, All FEs (besides the 410 and 428) were internally balanced, while FTs obtain final balance by adding weight to the flywheel or flexplate AND the harmonic balancer. As far as heads go, the FT has a larger combustion chamber and smaller valves and ports. On that 391FT valves are 1.75"intake 1.5"exhaust, the smallest valves of all heads in this family, giving this heavy truck motor improved low-rpm torqe but certainly not helping overall power much. Don't plan on getting 400hp out of this motor with stock heads. You can bolt FE heads to an FT block, but be sure to check valve-to-bore clearance, exhaust manifold bolt pattern for your application, etc. Check with Edelbrock and see what they have to say about installing their aluminum FE heads on an FT block. There are other differences and you should read all up on the subject before considering such a swap.  check "How to Rebuild Big-Block Ford Engines" by Steve Christ as a start. good luck.

I am aware of the 391 only in that I used to work for a heavy equipment shop and one came in to the engine rebuilder for an overhaul.  Not only are the cranks different to accomodate a pto, the bolt pattern on the back of the engine was totally different than any FE I have ever seen.  Granted, this thing was off of an 8 ton crane truck with a manual transmission.  That with the PTO would have accounted for the difference probably, but as I recall, it looked like the block was cast that way.

Another in the 360/390/428 family was the 352.  My uncles '67 3/4 ton pickup came with one, and it gave him lots of trouble free service.  He sold it to some guy with 120,000 miles on it and he put it in his Galaxy where it lived another four years.  I have no knowledge of the performance capacity of the engine however.  Since it isn't one of the garden variety FE engines, aftermarket pistons and other performance parts may be hard to find.  Good luck though.  I have done two 390 engines in my tenure, and they are just a good, strong, solid choice for a Ford build-up.

Actually the352 is a garden variety FE,in fact was the
302 of the fe family as Ford used it as a base motor in everything big from the late 50's til mid 60's.

Performance wise,take the 360/390 block and toss in 428 internals to make a 410.Or bore it out as well(car craft
did this around 1998) and voila,428.

Or just bore out to 4.13 and 406.Lots of options.