Thanks Ted.

As a general rule and if switching from steel shim to composition head gaskets, you can mill the Y heads and/or the deck at least a combined total of 0.045” before having intake manifold bolt alignment issues.  If milling any more than that, then the intake surface on the heads will need to be cut 0.014” for each additional 0.010” cut from the heads or deck.
 
If your heads and/or decks have been clean up milled, then I’d be more concerned about the original angles staying in place during the milling operation.  I’ll suggest sitting the intake manifold on the heads without the gaskets in place and insure that the angles at both the heads and intake manifold match up to each other.  You’ll want to look at this from both a side to side aspect as well as front to rear.

Lorena, Texas (South of Waco)

Think I've found my problem. Got car running, idle at 800rpm, timing 12 degrees. Nasty stumbly erratic idle. Vacuum gauge bouncing all over the place ( rapidly). Above idle gauge is steady. Sprayed some carb cleaner around base of carb, engine stumbled massively, also sprayed around intake manifold gaskets, engine stumbled badly , vacuum gauge went nuts bouncing between 12 and 16 . Think i got a few leaks. Suspect I'm gonna have to mill the manifold but with not knowing how much the heads have been milled I think I'm gonna have to take off a bit at a time until it looks something like.