May be a little bit late being you’ve bought stuff already, but if truely I decide yet let me list a few things for thought.
1: you said a cruising vehicle, as much as I like manuals they aren’t just cruising transmissions, put an auto in drive and cruise. Also if you’re married and your wife ever needs to drive it for any reason. Can she drive a manual?
2: SM465 ratio is so deep 1st is useless and no overdrive, unless you go with a highway rear gear to drop RPMs.
3: 700r4 & 4l60e both have the same ratio so sbc or LS you can compare trans the same way. 1st gear is a 3.06 ratio vs sm465 2nd 3.58, which you use as first. So not much different starting out except with an auto you can ease into motion with something heavy and not be hard on the clutch. Then again how heavy will you be pulling with a blazer.
* side not you already have a 27 spline np205 which matches a 700/4L60
4: NV4500 is somewhere around 5.4 1st if I remember correctly, similar to the sm464 but with overdrive.
Engine
1
epending on where you live and emissions laws old school may be a little more of a pain to meet standards
2: If going old school and wanting to stay correct to the truck, can get pricey if you want all parts period correct. But ultimately the simplest
3:carb vs efi Offroad, normal Offroad no difference. Hard angles and steep grades aren’t affected with fuel injection
4: ls drivetrain is proven and in millions of vehicles since mid 1999 with hundreds of thousands of miles, and if staying with a stock setup you don’t have to worry about maintence anymore than the next guy driving his used Silverado.
Personally if it was me I’d get a used drivetrain from a trailblazer 4wd or Buick rainier awd and have the computer flashed just to delete downstream O2s and anti theft. Keep in mind unlike the trucks they don’t have a TAC module and makes gas pedal compatibility a lot easier. Also all 5.3 trailblazers, rainiers, envoys, and Saab 9-7x used an aluminum block and the 4l60e which you have a transfer case already for.
Now at last if you want a play toy that’s cheap and fun but not to concerned with comfort and cross country reliability/parts availability, extreme cold weather starts and go. Go old school carb with the manual.
By no means am I saying carbs don’t work reliably, just looking at overall conditions and parts availability.