Thanks for the thoughts!
I have been looking around the internet for a Marlin 1895cb in 45-70... But they're out of stock everywhere and I don't know how much I'd trust the new manufacture models they'll have later this year right off the bat... Kind of like buying a first year car, and Ruger may not continue producing the entire Marlin line.
I'd planned on very likely using Goex OE or Swiss black powder. No risk of over pressure, usually cheaper than smokeless, and apparently this is where the 45-90 (and maybe 45-70) really shines. I'm not worried about having to clean immediately after a shooting session to prevent corrosion. Smokeless loads in the 45-90 require a filler wad in the case.