[campusfive]

I haven't been able to find examples of vintage 20's-40's strings that are actually that big, and I've been looking.

Considering you need significant acoustic projection (for the ear trumpet), but need to maintain the possibility of playing electric without a massive imbalance problem, it's seems like Monel would be ideal. Martin Retro are the only production monel roundwound strings. (Flats weren't common until the mid 50's, and generally neuter the acoustic projection of a guitar).

Besides being the dominant string metal during the early and mid 30's, Monel strings still sound and project like "acoustic" strings, but are much better balanced since they are closer to what we think of as nickel "electric" strings. Bronze started to take over in the mid to late 30's since it has increased projection and fullness. My 1937 ES-150 would have shipped with Gibson Mona-Steel strings.

I love the sound of monel on my '32 L-5 (which would have shipped with monel as well), but I generally keep Martin SP 80/20 on it because I need the increased projection. Oh, and Martin SP's a really reasonably priced, and I like keeping fresh strings on my guitars to maximize projection and acoustic response.

As far as gauges, some guitars don't really benefit from strings larger than 12's, but it depends how lightly built they are. An Eastman 610 would probably benefit from 13's, but you could try 12's. But +1 for bumping up the gauges of the high E and B. I use a 14/18 with a set of either 12's or 13's depending on the guitar. I find they balance much better acoustically.