Looking at a standard LA cover against the Desoto block, it seem that a little cut and weld around the water passages and two ears at the bottom are all that would be needed to make the cover a simple bolt on. It's surprising how close everything is.
I made a mold and had 2 timing covers cast. Here's the one that hasn't been machined yet. It takes a 318 pump. It was a little thin in the back and had to be welded shut. The mold will be modified to cure the problem.
