Any non-extreme black powder load should be safe for a steel-framed Remington repro with a conversion cylinder. However, heavy bullet .45 loads at anything over blooper velocity will produce significant recoil. If you are used to shooting a Ruger Vaquero, or other solid, substantial gun, the lightweight Remington with full-house BP loads will seem like a whole new animal.
Will full house .45 BP loads driving a 250, mine tend to batter the knuckle behind the trigger guard and muzzle flip is pronounced. Compared to a standard 24 grain round-ball load, recoil is snappy, to put it mildly. The modern repros are not made for heavy loads, and such will eventually shake things loose.
To prevent battering you or the gun needlessly, try a moderate load like a normal C&B charge of powder, a 180gr LRNFP, and filler like Cream of Wheat to bring the load to full volume. My Remingtons seem to shoot much more accurately with light bullets. I have also loaded .45 cases with a C&B charge of powder, filler, and a .454 roundball, essentially duplicating in a cartridge what I load in the C&B cylinder. Depending on the powder, BP or substitute, you can include a pre-lubed felt wad in place of some or all of the Cream of Wheat.
Note that BP cartridges require full-volume loads, never leaving any open space in the case. This also applies to BP substitures.