I have an '81 Silverado with a 350 out of a '78 Cheyenne and a bum TH350 . I have the oppurtunity of replacing it with a TH700R4 (it's free by the way and is a Goodwrench). I've been by some that this combination will not work because of the gear ratios (poor performance, mileage...). The transfer cases are geared the same but it has the 12 bolt rear axle. The first year of overdrive trannies ('82) from what I have seen in my '82 uses the ten bolt axle. Will this work or are there some ratios that need to be changed and if so, where.