theres a old sitting '89 1500 5.7L 350 out in the field and went to go start it..hasnt been started in two years...changed oil and coolant...primed oil and rotated engine while priming before attempting to start it...moved nicely...started beautiful...but 10sec after starting...a loud knocking came from the #5 and 8 cylinder area...checked things out but cant seem to come up with the problem or solution...hoping its not the rockers out of adjustment...dont know didly about rocker adjustment...any ideas?  

First find out exactly where the "knock" is comming from..top or bottom end.An easy way to find out is remove the valve cover,start the truck,take an old piece of heater hose(foot or so long)put it to youre ear and touch it to each rocker stud(use it like a stethescope)if it is a rocker you'll know right away,the knock will stick out like a sore thumb,if thats not it get under the truck and run the hose over the oil pan if its in the bottom end you'll know.As far as rocker/valve adjustment goes there are 2 easy ways.
1:get some rocker stoppers from a parts store,they only run a few bucks.Remove the valve cover(i start on the driver side)the stoppers have a plastic "tit"on one end,that goes in the oil hole on the rocker,so you dont take an oil bath.Clip them on all the rockers on that side,start the truck.ONE at a time loosen the rocker nut till you hear a "clacking" sound then SLOWLY tighten it back till it stops then go a 1/4 turn,repaet for other side.
2:starting on the driver side(again thats just what i do)remove the valve cover.starting with #1 bring it up on a compression stroke(piston all the way up both valves closed)loosen the rocker nut,put a 0.002 feeler gauge between the rocker and the valve,tighten it down in small increments till the gauge moves in and out with a bit of drag.Them repeat these steps for all rockers.
Hope this helps,let me know how you come out.  

Yeah, gotta find out where the knocking is coming form exactly. It could be any number of things.

Why was the truck parked in the fiel to begin with? Any previous issues you know about?