Quote Originally Posted by sleeper1500 View Post
It's the same transmission, keep in mind the 4.3 is still old style SBC instead of LSX, so the NV3500 in my '06 will be the same as the one in your '89. Physically anyway there may or may not be differences in ratios and what not. I know S10's got different ratios, and the NV3500's Dodge used seem to be holding a lot more power (I'm still looking into whether or not there interchangeable with a simple bellhousing swap)
although his transmission & ours are interchangeable, ours are actually a little different than his. the newer ones (93+) have a single shift rail (instead of 4) and different input shaft bearing arangements

the fullsize GM transmissions have the same ratios across the board

Dodge transmissions will not swap with GM models - i actually spoke with a bunch of people including the manufacturers about this last year (i wanted to get a dodge NV3500HD for my 5.3 swap). the bellhousing & transmission case are one piece & the different makes have different bolt patterns. they also use different input shaft lengths, spline counts, and pilot sizes. the output shafts also have different spline counts.

you could swap s10 & FSC transmissions, but since the s10 tailshafts are longer, you'll have to move the crossmember and get a new driveshaft