Congrats!!
If you look at the factory Rem 405gr load, you'll notice they're crimped on the ogive, not in the cannelure, they also have a COL of 2.532", the discontinued PMC ammo is 2.535" and will shoot fine in any Handi/BC. You may also have one that's an exception to the rule, but there are countless threads here on short throated .45-70s, both BC and Handi, I have 4 of em, they were all short throated, the 45-120 is the only one I didn't throat for obvious reasons, it got a super long throat after the rechamber!!
One of the benefits of throating is you can load much longer with the heavier bullets which will reduce pressure, a good example of this can be seen in Hodgdon's 45-120 data for the 500gr cast and H4895, 60gr at 1809fps, a similar load in a .45-70 cartridge would put pressure near 40kcup at a COL of 2.85", the 45-120 pressure is 28.5kcup. So if you're interested in loading big bullets, there's a big advantage to having a bit longer throat in a 45-70, but not so much if you shoot the lighter 300gr bullets.
Tim
