[rotorwrench]

There were several tools made that really speed up the process of removing crusty valves. KD made a good one to pull the valves but it is easier if you have a good tool to yank the horse shoe clip out with. The puller will then just pull the valve assembly right out. I use the All Power tools to do most of them but I still have to use the KD tool on some. All Power made an excellent clip puller and a wedge tool that forced the valve up by whacking at the wedge with a slide hammer. There are other tools available that work too but those are the best I've found so far.

On 21 stud differences:
If a person sticks to the later 37/38 21 stud design, it is very close to the 24 stud that followed. The early ones had bolts that went through the tappet galley on through the main cap to bolt them main caps on with nuts on the bottom side and there were different size main bearings on some. I think an 8BA type would work for some since it can be adapted with the Mercury and truck half bells but you have to use the Mercury or truck type oil pan too. Others still might want the early block type with the integral half bell on the back and use the early type vented oil pans to make them look more authentic.

I'm fortunate that I don't have to make those decisions. They aren't easy to make.