Not sure how helpful this is, but I'm working with an Exogram crank and trying to find a compatible 46 tooth outer ring. The problem is different than yours, but an observation of the Exogram inner ring may be of help. The Exogram inner is machined and relieved to move it closer to the outer ring by nearly 1mm compared to earlier Powerglide inner rings.

If I were doing what you're attempting I WOULD NOT attempt to thin the ring mounting tabs. It's a great way to ruin a good carbon crank. I'd take the inner ring to the lathe (or local machine shop) and relieve the inner mounting face by .020". Not sure this helps but it would close the gap to Exogram specs. It still may not work as desired as the Exogram rings are designed to work with YAW derailleur.

Then there's the thing with the hidden bolt vs non-hidden bolt crank style. The inner and outer should be matched for best shift performance.

You may be stuck with a 34 or 36 tooth inner that is compatible with the Exogram outer.