I don't think the in-the-well IFR position is as subject to reversion as the top position.
Again this is more radical than anything I've dealt with. So I would go want to see what is repsonding.
a. Exactly as it is, stick some wires down the secondary IABs. See how the AFR, vac and engine responds.
b. Open the primary throttles a 1/4 turn, and close the secondary throttles about the same.
- then see whether the idle mix screws are responsive
- try (a) again.
c. if opening the primary throttles and decreasing secondaries increased engine rpm, then reduce secondaries more or reduce timing a couple degrees.
There's nothing sacred about a square transfer slot. It's just an easy way to visualize a typical starting point.
(I'll cross post to RFS later if the discussion hasn't already moved beyond)