my brother had a 76 GP with the really lo-po 400, like 8:1 compression, and it was pretty damn quick for a big stock as hell heavy ass pig. from a stop i'd could barely take him in with my old 70 cougar that had a stock 351 with only an e'brock intake, carter 600 carb and 2-1/4" dual exhaust with stock manifolds. i'd definitely say that your buddy would smoke your ass and then it hand it to you when you finally got the end of the strip. at minimum i'd say you need at least better heads, different cam, and a better suspension more suited to the drag strip. ditch the swaybars front and rear, run 90/10 shocks out back and some cal tracs bars. you'll need gears and and some sort of locking diff, either a trac-loc or detroit locker and some meaty drag radials or some M/T sportsman pros. up front run the stock suspension but use some 70/30 drag shocks. consider sub frame connectors required equipment as well. alternatively to removing the sway bars you could just disconnect them.
if you really want to beat him consider a 393 or 408 stroker and 150hp shot of N2O.