^^ Sorry dude, you dont know much of anything about turbos.
You can easily have a turbo that spools at low rpms, and you can also use any turbo on any motor. You would need to build the piping for it, and build the motor for it. Guys have been racing AMC 258's for years, so I would look into the car side of things because I am sure it has been done.
I wouldn't do it, but if I were gonna, I would be looking into main bearing studs, high strength rod bolts, and a ported and polished 4.0 HO head with studs. You could probably run 8-10 psi safely on a completely stock motor, but no more than that. Cheapest way to do it would be a remote mounted wastegated "tailpipe turbo" setup.
While it is possible, I would never do it due to the complicated nature of the setup. I like my stuff simple when I have to troubleshoot it on the trail.