So easy to spend other peoples money..lol
the o/p said budget,, it is a truck it's a c-10 so 2wd mostlikely 4000 lb's ish just like my 71 (mine is a long box, short will be less)
o/p said he wants 400hp at the wheels, let me burst your bubble,
you will have a hard time getting that power to the ground with the factory leaf spring set up as is.. plan on spending bucks here..
400 bones isn't bad for a known running 350 you can get it running now without pulling it apart.. it's not that hard..
it being a 300hp 350 means zero if you are going to rebuild it..
other than check to see if it's standard bore, a 4 bolt block and forged crank..
if it's not as above ,any 150 dollar 350 core will do.. as you'll only be use'n the crank/rods/sheetmetal/head castings(maybe) and the block..
if it's got a forged crank it's worth every pennie of the 400 bones..
rethink this, shooting for the stars is nice.. but an honest 300hp to the wheels will make your truck FLY.. if it hooks..
these trucks are not all that heavy compaired to later trucks..
if use'n a 3spd auto ,use'n a th350 will get a few more to the wheels than the th400..
if going 383, the worth of your bud's 350 is really zero..
as I'd want to start with a standard bore 2 bolt block and add splayed main caps..