Not saying the RM can't handle it, just saying I'd be worried about the gun getting loose over time, battering the wedge, arbor stretch. A full house 45 colt with 38 grains of 3F and a 250 grain bullet is a stout combination. The weakness of the open top design is that every time you fire it your trying to tear the barrel off the end of the arbor. Don't get me wrong, I've got a bunch of colt designs and love them. My load for mine is (without checking my load data) 28 grains of BP and a 200 grain big lube bullet in 44 colt. The Uberti RM is slightly larger than the original to chamber 45 colt, the original would sometimes break through the locking lug on the cylinder in 44 colt. Still doesn't mean it can digest a steady diet of heavy loads without shooting loose.
A SAA is a good bit stronger with a solid frame, but even they can shoot loose over time with heavy loads. My basic load for all my 45 colt stuff, and this includes a 1860 Henry, is 36 grains 2F Graf's BP and a big lube 250 grain bullet.
About as much as I can stuff in the case and still seat a 250 bullet so it'll function in my Henry is 38 grains 3F. That's also a good short range deer load out of the Henry. That comes close to the original loads, if you could get your hands on old ballon head brass you could replicate the 40 grain load with 2F swiss and less compression.