Shane,

I don't know if all the 16 gauge Aubrey/Meriden guns had scaled frames, but I have owned two and both were a little narrower across the breech than my 12 gauge guns.

Firing pin spacing measures 1.090 on a 16 (S28 S.N. 70163) and 1.160 on a 12 (K28 S.N. 38419) for about 0.070 difference. Fence width is also 0.100 narrower at 2.220 and 2.320. The standing breech is about 0.060 shorter too.

The 16 gauge guns do show up occasionally, but like you, I have never seen a 20.

Hope that helps,
Steve