Like your plans, but...
Like your plans to off road with a buick engined crawler, I regularly take our land rover DII off road and have messed with buicks for the last 12 years or more. I do believe that these guys are pointing you in the right direction with regards to your engine/turbo config.
The original turbo you found is way too big for any application with a 3.8. As previously posted, torque wins races especially in off road situations. I found this out by putting too big of a cam in my land rover 4.6. The stock cam would make more low end torque, which was better for crawling than reving the engine to get up steep ledges and slopes. After the cam, the bottom end torque dropped off a bit and made it a bit more of a slug without leaning on the pedal. My stock DII will rather crawl over things with ease, with less pedal effort than my built 4.6 with a cam and ported manifolds and such. Just saying. . .
Your driveline is going to eat up tons of power, rockwells? They are strong as hell, but work on maximizing your torque from idle up to 5000 RPM if you want it to work out well. Dont expect a high stall torque converter to help you at all off road, it will cause the car to be a slug without heavy throttle input, and will sacrifice more power/torque where you need it.
I think the best thing to do is to install something like a TA49 turbo designed for a grand national, which provides near stock spool up, and produces up to 500 hp at 20psi or so if the heads flow. This is usually achievable with stock internals, stock camshaft, and basic fuel system upgrades and airflow improvements. The power curve will be BROAD and have LOTS OF TORQUE whenever you need it.
OR< run the full SC3800 setup and blow boost into it with a slightly bigger turbo like a TA62 or something similar. Have you seen a detroit Deisel 2 stroke V8? Uses a big roots blower for off the line torque, and a big turbocharger blowing into the top of the supercharger for more oomph once its spooled up. The size of your axles and tires puts you in a category to need off idle torque like a semi truck, not top end HP like a drag car.
I think these are more realistic approaches than a monster diesel turbo on a 3800 motor, buicks have had aftermarket turbos for 25 years that will be better suited to your needs than any diesel crap from a junkyard will ever be.
Good luck with everything and hope it blows the chevy's away!
