John,  I can say that trying to fly an approach in turbulence with compass, TC, and altimeter is a serious pain.
Doing the same with a functioning DG is 5 times better.
....but I don't know if that is your question (what's an AH?  did you mean AI?)
AI + portable GPS is probably doable, especially if it's a 396.

My personal requirements are that I can fly an hour with a total electrical failure or vacuum failure.
The Chelton's, gns430 and trutrak are a flunk because they are plugged into ship's power.
A battery backed mechanical AI + 396 + portable com is my solution.

(okay - actually I have vac dg and ai in addition.   how many times have you rebooted your ai this year?)