Don, without actually mounting a degree wheel on the front of the crankshaft, it's an educated guess as to where timing marks are going to be on a particular engine. Even the engines with more accessible timing marks than a stovebolt can have timing errors due to manufacturing tolerances between the crankshaft, flywheel, bellhousing, etc. Does your timing light have a delay-flash feature which allows you to dial the timing flash back to zero with the engine running? If so, all you would need to do is find a true TDC position by using a positive stop on the #1 piston. Someone else just discovered that the positive stop rod inserted into the spark plug hole needs a bend in it to actually be able to reach the piston crown. If you need information on making the stop fixture and doing the checking procedure, drop me a PM- - - -it's a pretty detailed process.
Jerry
