I have a 292 in my 78 GMC 2.5 ton. It used to be an Asplundh chipper truck. I installed a cast iron header set fro Langdon's Stovebolt and a pair of carburetors from a 1979 Honda CX 500. The performance level is fabulous! The I added a Brownie behind it. If you want to keep costs down, get performance and mileage, I'd lean toward building a 292 from the bottom up. The intake would have to be custom if you want to retain that updraft, though.
Even if the suspension will take the weight, you'll be asking more of the brakes than what they were designed for. You'd also want to put a sway bar on it in a big, big way!
Wait a min... I recognize you. I watch you on YouTube! Nice to meet you!

Yeah, I remember the Brownie setup you installed. Spicer 5831, wasn't it? Ol' Jimmy sounded pretty mean without a muffler! Mine's the smaller 5531, a Spicer-built Brown-Lipe. This'll be a bit down the road, after I fix the roof leak and the rust it's caused, but I'll be doing the same - installing it in place of the carrier bearing. Need new driveshafts and companion flanges for Spicer 1350 U-joints (smallest I can get flanges for), so I figure it'll cost about $1500 to do it all.
I'll be tearing down the trans this weekend, see what I'm looking at for parts. Feels like at least one bearing is getting rough. Gears and clutch collars look fine, aside from a touch of surface rust. Pics and maybe a vid to follow!