get rid of it,the money you will spend isn't worth it.
but....make sure the timing chain you buy has the slot for the woodruff key right on the dot for the timing,mill the heads and intake .30-.40 works good
intake has to be milled to line back up with heads milling it isn't gonnna do any thing for horses.4bbl gas gusling non efficent carb should do the trick on top,waste some money on a over priced intake,some shims for the vavle train and a cam somewhere around 270 280 adv dur,just call up your cam manufactuer of choice and ask for recommendations.
you are gonna be disap[pointed with the performance of a built 400.buy a efi 351w and be done with it.all kinds of power, EFI,plenty of aftermarket parts,and you will get better gas mileage.if you can afford to build a 400 you can afford a 351w and adapter plate from summit or jegs.
ever wonder why nobody swaps in 351m or 400's?(why most people don't swap)