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1986 CUCV
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Hey Guys

I did a rebuild of my CUCV last year. Long story short, it was gas swapped before I began. I bought a new vortec 350 and put Holley sniper EFI and dual sync distributor. I’d like to be able to tow a 10k pound trailer (flatbed and tractor) on occasion more comfortably. I have come to the conclusion that low rpm torque is my primary obstacle.

I’m not looking to be fast or roll coal. I’d be happy with a healthy, mild 12v Cummins. I see many options for running 2wd trucks for a decent price, but running 4wd trucks are really pricey.

Will a 12v Cummins bolt to my th400 without smashing in my firewall and sliding everything back? I’d like to be able to revert it to stock trim with a j code 6.2 if wanted. I’d be fine with setting up the th400 to accommodate the early torque delivery. Has stock D60 and 14 bolt full float, but regeared from 4.56 to 3.73 which will work better for the Cummins I’m sure. I’ll be respringing the front for the weight and running 35” tall tires.

...or am I dreaming? Is the full running gear from a donor truck (trans/tcase) the only way to go? Is it possible to shoe horn this deal into a square-body without major body modifications?
 

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Welcome to the forum. Mating a 6bt 12 valve to a TH400 isn't a good idea. Two main issues are no OD gear so you top road speed might be around 55 MPH or less and second that transmission won't stand up to a 6bt with any kind of power mods. A bare bones unmodified 6bt was 160 HP with 400 lb ft of torque. The peak HP is around 2500 RPM but the peak torque is around 1600-1700 RPM. You can raise the RPM limit on the governor but the torque continues to drop past 2000 RPM. So if you tune the 6bt to around 200 HP which would be easy, then the torque would be up near 500 lb ft which is more than a big block GM. A few guys are running the GM 4L80e on a 4bt and maybe one or two have it on a 6bt. When GM went to the Duramax engine they used the 4L85e for a while but the power output was limited. All later applications used the Allison 1000 5 speed or 6 speed. The full engine/transmission/transfer case transplant may be the better option. Is your truck front axle passenger's side or driver's side drop? Dodge had passenger's side for a while using the NP205 and then changed to the driver's side using the NV241D or NV241DHD. Dodge also had a wide range of automatic transmission with OD. The 46RH and 47RH were mainly mechanical and then they went to 47RE, 48RE,etc which are computer controlled.
 

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Yes Dougal, towing a heavy load like 10,000 lbs takes a properly prepared vehicle and driver. I learned towing from a friend who pulled a 27' travel trailer over 100,000 miles. All of the pickups I've owned were setup for towing. I had a class 3 or class 4 hitch mount on the truck, electric brake control, load leveling hitch, dual sway controls on the hitch, 4 wheel brakes on the trailer, and a emergency break away system that would lock down the trailer brakes should it become disconnected from the vehicle. The one big thing is to be sure you have adequate braking on the trailer. I got rear ended one day at a stop light by a guy in a Dodge 3/4 ton towing a Bobcat on a trailer. He didn't have enough brakes and hit my rear bumper. No major damage to me or my truck but it took out his radiator. My F250 4x4 was a bit taller than his 2wd Dodge. The last 2 trucks I owned came with factory wiring in place for towing so all I had to do was add the brake controller, hitch, and trailer electric receptacle at the rear.
 

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your truck is pre-88? For what its worth, I swapped a 5.9 into my 97 Suburban, along with a Dana 60 frt and Sterling 10.5 rear. Didn't take much at all in the way of mods to fit the engine. No firewall mods at all, only tweaking of the core support. That was primarily due to my truck having the quad composite headlights. That was 10 years ago. I am now in the process of swapping my 5.9/NV4500 and axles into another 97 Suburban. This time around I am using the W/T front grill to gain the additional 10 inches between the headlights, to make the intercooler an easier fit.
 

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Member Rube Bonet might be of some help as far as engine mounts and replacing the front crossmember. GM truck front crossmembers have to be modified to clear the oil pan on a 6bt. Rube did a 6bt into an '86 Blazer several years ago that was a work of art. Here's a listing to his business site showing his kit for the '73-87 GM. This is a weld on kit, not bolt on. 73-87 Chevy K Series Cummins Motor Mounting Kit
 
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