If you use an NV3500; make sure its a 1993 and later C/K truck. For the 3500 the ratio you want is the M50 close ratio with the less snoozerific 3.50 1st gear. I do NOT know if the 3500 available in the C/K trucks was ONLY the wide ratio with its 4:1 1st gear. I also do not know if the 4.3L V6 mid 90s S10 3500 (the common spot for a M50 close ratio) is able to fit the V8. The 3500 has an integral bellhousing (like an automatic) and I do not know if there is enough pilot length for a Gen 1 V8.
Re: the 4500; Its a 'better built' unit to be sure; its built for a working truck to tow loads; Its literally a 200 pound chunk of cast iron and has a charming 5:1 1st gear or the utterly re-donk-ulous 6.34:1 1st. Which means probably just use 2-5 gears. AND if you're only going to use 2-5 to begin with, you might as well find an 833OD. Easier to fix, smaller, 4spd OD
A NV3550 out of a Heep is NOT the same as the Mustang 3550; its a POS so avoid it (yes I said Heep).