Will an entire G1 drivetrain from a 69' SB pickup, fit on an 85' Blazer frame?

[Chevy1TonFun]

There are major differences between 1st gen and 3rd gen. I would also take only what you have to from the 69. The axles will swap. The springs are different lengths for 1st gen to 3rd gen. I don't believe the shackle flip will work. The frame is different on the 3rd gen, so the cross members won't work either. Your original 3rd gen cross member should work, its the same tranny. Why change it to a 69'? The triple stick you will have to trim and cut to make that work. I'd say jump in and take the issues as the come. Good luck and hope that gives you a start to all your questions.