GM builts thousands of full size trucks and vans with the 4.3 engine in them so your size and weight is not a problem. All the 4.3 1986 vans that I worked on came with the 4bbl Quadrajet which is probably as good a combination carb as there is. If you keep your foot out of it and run just on the very small primaries it gets decent (but not great) mileage. Kick open the huge secondaries and they scoot hard as the gas gauge plummets.
