Chevy & GMC Vans

With the engine compartments being small as they are in the General Motors M-body, I'm looking into contingency gearboxes and axles for the Cummins® Repower™ R2.8-161, a reasonably complete 503#-weighted installer package built around the ISF2.8c-161 cam-in-block/two-valves-per-rocker-arm inline four (161 HP @ 3600 RPM; 267 ft-lb @ 1800 RPM). The 1800 peak-torque RPM of the ISF2.8c is much lower than the 2400-2800 peak-torque RPM of the Chevrolet and Pontiac gasoline engines used in Astro and Safari production, therefore favoring the taller axle ratios with stock wheels and tires. Example: Whereas I've a 9" Currie full-float with 4.11:1 R&P shortlisted for my M11006, which has the stock V6-4300, the ISF2.8c-161 would need more like 3.07:1 R&P to hit 1800 RPM @ 55 MPH on my 215/75R15 100S all-seasons.

TREMEC® (MEX) has a few candidates for the repower gearbox. The TR-3160A (4.12:1 first, 0.80:1 sixth; 296 ft-lb capacity) is probably a satisfactory fit for the RWD model. The TR-4050A (6.16:1 first, 0.76:1 fifth; 425 ft-lb capacity) is optimum gearspread for the ISF2.8c and short and light enough for off-roading in the AWD model, provided that a satisfactory transfer case (e.g. a remanufactured New Process 205FM) is used. Any contenders from Zahnradfabrik Friedrichshafen (DEU), Tōyō Kōgyō (JPN), or other transmission manufacturers to complete a repower?

I personally hate diesels, they stink, are slow, sound like they will come apart at any time and release more toxins that hurt humans then any other engines out there. Help me understand why you would want one in an Astro/Safari?