Just saw this on fortunecookie45lc you tube site: Lee micrometer bullet seating die. A recent addition to the Lee reloading die collection.
According to fortune cookie, this die can also serve as a hack to create precision crimps.. Which may be useful, in your case.
He demonstrated it on 9mm cartridge. To show how easy it was to get a good, easily repeatable taper crimp. But, may also work well for roll crimps, too. The die is available over a wide variety of calibers. Including, .45-70.
Easy to use. Screws onto existing Lee die. Provides precise control of bullet seating depth. May also provide precision control of crimp. I can see where this would be a great benefit with cartridges that are sometimes finicky to crimp...ie: 38-40, 44-40 WCF.
Or when returning to a previous bullet seating (or crimp) setting. Allows for easy set up
Not sure whether this may be of use in your case, but might be worth a look.
By the way, though I've used both RCBS and Lyman 45-70 dies in the past, I've found that the Lee factory crimp die delivers good results. I use mine with lead bullets in .45-70. No issues. Gives me a good, firm crimp.
Will be looking into this Lee die myself, in the near future. Can already see where it would come in handy.
Al