Anything from 1999-2006 is going to have the non-AFM LS engines. A few nuances will push you towards 2003-up. You have four engine sizes to pick from, 4.8L, 5.3L, 6.0L, 8.1L. Obviously bigger is better for making power, but it depends on your goals. The 5.3 and 6.0 are the most common in the trucks. I’ve got a 6.0 in the 2500 Suburban, and it has plenty of power on gasoline. Way better than the old 350 in my older 1500 Suburban. I’d love to try a 6.0 in a lighter vehicle on woodgas. I also think a 3/4 ton with the 8.1L should rival a V10 Dodge on power output, for a fantastic woodgas work truck.
As far as vehicles, there are plenty of stock vehicles that came with LS motors. Obviously the pickup truck format is the easiest for woodgas. Anything else we’ll have to get creative, like I mentioned with bumper mounts or trailers.
And then there’s swaps, like Steve points out there are tons of people LS-swapping everything you can think of. I have a site bookmarked, seems to be dead now but the wayback machine saved it, this guy figured out all the details for putting LS motors into our Dakotas. Could be interesting for a testbed, the truck itself is a known quantity.