[Zoomad75]

I'm going through this right now on my 91. Back up a little bit to my 75 and the 4 inch lift/shackle flip combo and NO changes made to the front or rear shaft. But that truck had a 205 case with fixed yokes and the slip was on the shaft. Now my 91 with the 241 case I did have to add a little length to the front shaft. The rear shaft on the 91 has about the same engagement as the OP's pics. Since we had to take the tcase back out again for a different issue, we'll look closer once we put it back in.

Keep in mind most driveline shops charge less to shorten a shaft then lengthen. Makes sense, less work. Adding length means retubing the shaft. So it might be cheaper in the long run, to find a shaft from a K10 or K20 that is longer and get it cut down. I did this on the 75 when I twisted the rear shaft in two after bouncing it off of a rock. I got a 3/4 ton shaft from a similar year truck and had my driveline shop cut it down to fit. Difference in price was almost $200 less to cut the long one down. Keep in mind the 3/4 ton shaft will probably have a larger u-joint but you can get a conversion u-joint.