i got a tremec 3550 hooked to my 351W. i really like it, and i got it because it's a proven tranny. they generally come equipped with a ford belhousing, but i remeber seeing a chevy option. it also has 3 shifter positions. they may have changed the name on them recently, but i'm sure you can find it with an internet search.

i'd stay away from a stock t5. they just aren't strong enough.

most all of the tremecs have a good rep. you can pick one out based on your HP. i started with a 3-speed auto, but went with my original choice of a 5-speed manual. it sure helps with the gas mileage and noise. the tranny is a little noisey, but it just feel really solid.