I am nearly due for my first valve adjustment, and just picked up a used factory manual. Looking at the drawing of the special tool, I think anyone with a drill press and some taps could easily come up with one pretty quickly. Basically, you would need to have the correct bolts to attach it to the towers, but the bolts that you would use to press down the valve could be anything of the right length, with a nut to set the depth securely. When I tackle this, I'll take some measurements and photos and post them. Maybe someone else that has already done this will read this thread and do the same.
I made one of those. Let me look to see if I have the drawings. It was the plate that bolted to the towers (from Woody's post) and the bolts with a contoured end that held the buckets down. Or PM me and I'll send you the tool to use and copy. I ended up pulling the cams since I needed to change a few shims and it seemed easier.
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