swap out the slant 6

hey, so im thinking of swapping my /6 to a 318. I have a 71 valiant 225cid, and i want to put in a 318 A block poly built from 1956-67. would this still work even tho its a different era? would everthing line/match up? im thinking i may also want to get rid of the 3-spd auto(lame) and put in a 4 spd. would doing this make the task easier? is the swap worth it money-wise to performance? or should i just put that money into the 6. i just wanna shred the tread! anyone have a comment? (ps: im only 17 so its a low-budget.)
(pps: tuners and ricers suck!)