eddybo, first question: I don't know, Ackley's handbook doesn't have case dimensions in it. I believe some loading manuals do have Ackley case dimensions. I do know tho, that if you sink a reamer deeper than it was intended, and it has any taper on it, the chamber will get loose. Second question: I don't think so if you're talking about a .280 Rem headspace gage. The go / no-go gages are cut based on a case head to datum line dimension on the case shoulder. The A.I. cases have a different shoulder angle than the .280 factory case. I don't think the headspace gages for the .280 Rem would give a correct chamber length reading on the Ackley chamber. Third question: yes. And if you build on a Remington long action, you've got plenty of room to feed out of the mag well with long O.A.L.'s. My experience with .280 Rem and 30-06 gov't is that the standard throat will get used up quickly, so you will need a custom throated reamer (or a throating reamer).
I would call Dave Manson and ask him the first two questions just to be absolutely sure. If he's there, he will take time to talk to you.
Let us know, Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time