[66gmcguy]

I just completed this swap on my 83 blazer, so I thought I would share my experience with it. I've heard from some people it's a direct bolt on swap with no frame mods needed (apart from the obvious issue with the bumper mounting), and other people say the core support frame brackets need to be moved. I discovered that the core support frame brackets are completely different, and are located in different spots.

The top of the core support frame brackets are flush with the top of the frame rail on the 81-87 trucks. On the 73-80 trucks, the top of the core support frame brackets are canted forward (relative to the top of the frame rail), and they are also about 3/4" further forward than the 81-87 frame brackets. Also, they sit just a hair lower than the 81-87 core support frame brackets.

I was completely unable to get the fenders to bolt to the core support when using the 81-87 core support frame brackets. I could get the top fender bolts in, but not the bottom bolts in (since the frame brackets were leaning back, thus causing the core support to lean back) The bottom bolt holes were about 1"-2" off. Luckily I had a spare 73-80 4wd chassis so I just took off the core support frame brackets and put them on my frame. I had to weld the old rivet holes closed, then re-drill new ones for the different frame mounts. Everything went smooth after that.

In all the forums I've read, I've never seen anyone talk about exactly how they are different, so I just thought I would post my findings and some pictures on here so anyone thinking about doing this swap knows what to expect.

1st pic is the 81-87 frame brackets. 2nd pic is the 73-80 frame brackets.

Lastly, this truck has a 6.5 diesel engine in it. I had to modify the 73-80 core support to fit the big diesel radiator in it. If anyone is interested in seeing some pictures of how I did it, feel free to message me. If enough people show interest, I will do a short write up about it and post it on here.