Hello Bullit.

Yes, just check it in park. Be sure to disconnect the vacuum advance, if it's connected.

If you reconnect the vacuum advance and the timing advances at idle (assuming it's plugged into ported vacuum, on the passenger side of the primary metering block), that's another clue that the throttle plates are too far open at idle.

And just for future reference, since you have a timing tape, rev the engine while checking the timing (vacuum advance still disconnected) and see how far it advances. Should be in the 35 degree neighborhood, I think. The guys running Edelbrock heads on small blocks can give you the generally agreed-upon number.

I also never asked - if you screw the idle mixture screws all the way in, will the engine stumble and perhaps stall out? It should if things are as they should be. Don't screw them in too tight (just enough to gently seat them), or you can damage the needles on the end.

Jim