These two are about the simplest HO vehicle kitbashes that you can do. The back half of both are Athearn models, and the front half are from CMW (Classic Metal Works).
The fire truck was the easier of the two. I was able to use the Athearn frame, and just needed to remove the bumper and file the gas tanks to get the CMW cab to fit.
The tow truck was more work, but only slightly more trouble, I did have to cut the frame and weld the CMW and Athearn frames together, so maybe not anymore trouble.