budget and handling a stout 350 are mutually exclusive...
Concur T5 not an option if you stand on it a bunch. BUT, any trans can handle any hp depending on how you drive it... Problem is folks tend to use the hp if they have it! T5 will work with a truck bench if it has an S10 tailshaft for fwd shifter position. Will not work with Camaro tailshaft - but tails can be swapped. You'd want at least a World Class T5 (mostly in F-bodies, but a few S10s had them)
Recommend scour craigslist for a TKO 500 (or 600) - but it's probably still more than you want to pay. In which case you may want to go with the some of the stock (stronger) options like the NV4500 - but I THINK that will require a hyd clutch setup - someone else can probably confirm - so figure that into your budget (and frustration....) when bouncing it off the TKO.
If you should decide on the T5 because you have calm driving habits, here's a link with some info. Not including for the content - but for the links in post #5.
http://67-72chevytrucks.com/vboard/s...d.php?t=480437
Good luck!