You've heard the argument for the best trans that you can get AND, it is quite logical argument/
Next question, what motor? That brings us to several different Qs.....Computer vs Non-Computer. How big?
You'll save a boat-load of money by not using a computer. AND, it will be way easier to figure out why it doesn't run riight. But, you might not ever have to do dat w/a computer (They run good, pretty much all the time)
There are several carbed motors that come to mind....150-200HP is plenty. For that matter, in a 1,200# rail, 125HP is plenty.
a 85-87 4.3 from a PU. They come w/a Q-jet manifold and a HEI, or one w/a TBI manifold (it needs an HEI and an electric FP, and 12V to run)
A 3.0 NIssan V-6 from a D21, or from any other w/an adapter or carb manifold (like from a 300Z, D21, Maxima, or Villager, a 300K mile motor)
A 350 up to 2002 only needs a manifold, HEI, (12V) and an electric FP to run. For that matter, any Chevy 4.3 or 350 only needs a carb manifold, an HEI w/12V, and an electirc FP to run. You can find the base for $500, easy. Then you need an expensive manifold, gear for the HEI and gas....easily under $2K.
A 302 Ford....is light, compact and available. I once saw a WaterPumper w/a 302 in it wheelie like a MF on Competition, w/Armstrong Tru-Tracs on it (street tires), then it rolled 3x on the way down. Easily under $2K
A 2.3, 2.4, 2.5 Ford Ranger 4 banger, reliable, and screams w/a big 2bbl on it.
The list goes on and on. All of the above can be had for under $2K, easy, depending on how you find it.... very possibly under $2K after being rebuilt.
BTW, I am not sure that I like the idea of a computer. But, if you do....Put in a STOCK MOTOR
Honda 3,something V6, like from an Accord or Oddysey (a 300k mile motor....the last one I had, in the last month that I had it, I almost hit a deer at 96, and at 291K-M it din't use any oil). These make as much HP as the 350 in my '86 Suburban did....225-250
EcoTec
Toyota V-6
2.2 Camry Motor....125HP, or more, stock
Honda 4 cylinder...there is one that makes 200HP, several have 16valves and make 125HP
Subaru, not a fan of them, but many folks are
Stay the hell away from a V-Dub....an unreliable money pit IMHO. For what a 2,000+cc motor costs, you can do a LOT better. I remember when they only used to cost a $ per CC. It is at least twice that now.
The list of good motors is quite extensive....but, if you are going this way....V-6.