[JJorgensen52]

Originally Posted by rs74

Just a couple of questions. Was it just going to be too much work to adapt the older cab to the newer frame to make it work verse the way you did it? Are the C30 frames similar in height and thickness as the ones from the newer square body? Also how do the 67-72 K20 frames compare to the same year C30 frames as far as frame height and thickness.

I ask because I know with the 73+ 30 series frames that are more stout than the 20 series. Just trying to put some things together in my head in case I get to do this to the 67 GMC C30. I have a line on an 85 K30 rolling chassis. I knew that it had been said that it probably would have been easier to use the 67-72 K20 frame but wondered if they were less stout than the 30 series frames either of the same vintage or the newer square frames.

I will answer as best I can, I've been away from the board with the holidays and call.

As far as I was able to tell, the late square body (mine was an '87) had a taller frame section in the center under the cab. I do think the '72 frame was a bit thicker, though. Either way, both trucks had a similar GVWR on the frames.

The major issue with doing a cab swap, to my understanding, is that there is a difference in the location of the core support - the square body frame is longer in front of the cab than the 67-72 frame. I did not compare the cab mount locations, but the square body's rear mount is definitely taller and would have to be modified.

The reference I made to the K20 somewhere earlier in the thread was with regards to hangars. The K20 and K30 trucks share their front springs, mounts and hangars. The sway bars are not the same, but the mounting points are.

So, my original plan was to buy axles and springs from a square body, then find a 67-72 K20 donor frame for all of the front hangars, etc. However, I happened to get a REALLY good deal on a complete truck with a rusty frame, so that made the most sense for my project.

I cannot verify this myself, but I believe the frames in the early square body K30 (1978 - 1980) is different than the 1981+ frame, which is ASYMMETRIC in the front, which created some issues for me with the cross members. Nothing undoable, just food for thought.