Bugger asked-How about the double 45-70 Remington imported from Russia.reamed to 45-90 plausible? Are they worth the trouble?
No, according to multiple gunmaker sources.
BTW, my .45-90 project was cancelled due to the untimely death of the gun maker. However, his estate did sell me one of his favorite hunting rifles, a Beretta .45-70 DR with 26 inch barrels. It shoots tight R&L groups at 50 and 100 yards and I have recently taken my first game with it.