They do bolt up just fine, but you run into problems with the speed sensors. The old TBI speed sensor is just a 4 pulse and the 4L60e needs a 40 pulse to shift. We ran into this when we put a 97 Votec and 4L60e with a NP208 transfer case. The trans wouldnt shift until redline and then it would shift really hard. We ended up drilling and tapping the rear trans case and putting in a reluctor and speed sensor from Jags That Run, but the 99 4L60e out of mine is different in the rear so that sensor set up wont work. Back to the drawing board.