I have a few suggestions to toss in.
A decade or so ago, GM tuned port injection "TPI" was the big thing everybody HAD to have. Now with the excellent LT1, LT4, LS1, & LS6 fuelie options, not to mention the aftermarket Holley Stealth and Lingenfelter Superram systems, the TPI has almost become the "red-headed step child" and been kicked to the curb. You can pick one up for just a few hundred anymore and you'll enjoy phenomenal torque and excellent 20 mpg-ish gas mileage. I had a 355 in my Corvette (10:1 compression, Isky 270 Mega-cam, 650 Holley on a Wieand dual plane) and swapped it into my IROC-Z Camaro making only the TPI change.
I'd say torque improved by about 80 lb-ft at the loss of only 300 rpm on the top of the rev band. Plus I gained about 3 mpg mileage too. Besides that, it's a GREAT looking set up. Torque is definitely more important with these trucks anyway.
About your rear end, you don't have to get those spendy Ford 9" and GM 12-bolt rear ends...unless of course you score one cheap at a salvage yard. Any GM 10-bolt from most 70's era cars (especially the F-bodies) will do absolutely fine with a torquey 350. And you can score a 10-bolt really cheap, with posi and a taller gear ratio for better highway cruising.
And another option with the transmission is the good old reliable Muncie 4-on-the-floor. Unless you WANT to run an automatic.
