cheapest would be a 5 spd out of a mustang GT in the junk yard. grab everything off it that you can. I think they run the T-5 right? all you need is a mopar bell, flywheel and clutch set up.

what's a junkyard T-5 going for anyway? $500? $800? it's gotta be cheap, since a brand new TKO gearbox can be ordered from Jegs or Summitt for around 1800.

if the 318 is not built up very much the T-5 should handle it ok, but the reason most people don't like the T5 is if you look at the torque rating, it's only good to like 300 ft lbs, and most of our Mopar engines are built up enough taht they far exceed that and require the beef of the TKO500 or 600.