Hi Mark,
A diagram would be great. I have a C-30, and the problem is I do not think the Moyer designed crank has enough clearance since my engine is surrounded by a box, so I have zero clearance in front & would need an extension as well.
I am considering a ~1" diameter hole that I can plug for the purpose of a visual on the roll pin for setting timing & hand cranking if I ever need it using a tool similar to the design you describe. No sense in re-inventing the wheel!