5.9 Magnum Torque motor build?

Having raced and upgraded a turbo car, I think you are off on a the wrong track with that for your low rpm TORQUE application. Having the lower 8:1 stock 318 compression ratio is just the start. For low RPM torque, getting the turbo to spool up at low RPM's is a very different matter. Using small turbo, having the impeller customized for quick spool-up and optimizing the cam are what you have to do... and sometime you have to tweak the engine compression ratio too. That's all on top of fabbing the exhaust, proper fuel pressure regulation, proper oil drain back system from the turbo bearings, and such... and it is all harder/messier with carbs vs FI.

This MIGHT have been solved...I have not looked. But most turbo work is geared towards higher HP and ignores the lower RPM torque.... so not suitable for how you want to use. And it is gonna cost you a whole lot more than you think in terms of money and effort.