r, long arms require long lop...
most pre war double guns would require stock aids to fit your needs...
https://www.amazon.com/s?k=shotgun+comb+riser&crid=1BMCMHB03GEXK&sprefix=shotgun+comb+riser%2Caps%2C441&ref=nb_sb_ss_saint-en-refocus-candidate_ci_hl-bn-left_1_18
Ed,
You are correct, most double guns I see listed are woefully inappropriate for my build. So much so that I have a hard time imagining who they would fit.
I was fortunate to find a pre-war English double that only required a slip-on leather pad to get me the length I need, all other dimensions were correct. My L.C. Smith however needed significant intervention to get to 15 1/2" LOP, DAC and DAH are close enough to work.