Can anyone tell me when GM made major changes to blazer frames? Also, are any of them substantialy stonger than others? I have a willys p/u body on a 1981 frame. The frame has cracked on the top behind the transfer case. I added a x-member there and it seems to have fixed that spot. It is now cracked on the drivers side top, just at the rear of the engine. This spot was kinked before i swapped bodies. I did a search but didn't find what I was looking for. Any info would be appreciated. thanks.