I think it'll live!
I've had the TH350 in my 74 K20 behind a 454 and a 400 small block for 15 years,and I plowed every one of those 15 winters with it with no trouble,till last fall I went to move it,and it had no reverse all of a sudden!--but for the amount of abuse I gave it,I dont blame it for croaking--those 2 motors are at LEAST as torquey as the 6.2 is,and it didnt phase it a bit!--and the forward gears still work fine,only reverse stopped engaging--I can still smoke the tires in all the forward speeds!..
I would use a TH350 with no hesitation behind a 6.2,especially if its only a driver and would not get used for towing or plowing--an add on cooler would be a good idea..if GM got away with the 700R4 behing a diesel and it lived,I'm sure the TH350, which is more durable than the overdrive's in my experience,will have no troubles-
Some prefer the overdrive to lower rpm's on highway driving,and the 1st gear IS lower on the 700R4--but not that big a deal with a diesel--you could put bigger tires or get away with 3.08 gears and still have good pulling power with the 6.2,and gain mileage to boot...
Youll need a vacuum pump to run the modulator valve,any 6.2 that had a TH400 will have one,and the switch to control the vacuum--700R4's have no modulator,so no vacuum needed for them..
(My vacuum switch was pooched on my 6.2,and I havent seen a good one yet in a junkyard,not sure if you can still get one new-- so I ran the vacuum directly from the pump to the modulator,and screwed in the adjustment screw on the modulator all the way in--it shifts rather early and soft,kinda like grandpa's caddy!--but it hasnt seemed to hurt the tranny after plowing all winter--if I want fast acceleration I just downshift it manually and let it wind up a little more--
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