[Brian]

Russ, you said in your earlier thread that this is an Isky 77B grind.
The specs for this cam state inlet opens 19* BTDC and ex closes 19* ATDC.
So, at exactly TDC, both valves should be slightly open should they not?
OK, you've located TDC. So you know where the crank is....now you need to degree in the cam so you know where it is.
And then, when cam timing is correct....since the distributor is driven off of the front of the camshaft, if timed up correctly on a timing fixture, the ignition timing will be right!

I still reckon you're one tooth off on the camgear/crankgear, that advances everything 16 point something degrees [crankshaft degrees]. Then, I dunno how your distributor is set up, but it could quite conceivably be advanced, adding up to the 25* you're seeing at idle.