Experienced exactly the same problem (and found the same solution) with the shell holder ...
I seem to recall reading that the cartridge OAL is fairly critical in the 1876 action but, in the hope of avoiding both 'overshortening' the cases and crimping over the front driving band, I'd just try to load a few with a greater OAL and see how they cycle (and if they chamber fully, which could be another issue with a longer cartridge.) If not, just pull the bullets and you haven't lost much but a little time ....
On the other hand, since the minimum case length given in the above specs is 1.80", I can't see that shortening the cases to 1.76" would be too problematic. Alternatively, since that is only a 0.04" difference, maybe you could 'combine solutions' (i.e. shorten to 1.80"
plus seat the bullet as deep as possible without actually crimping on or over the driving band) to stay within the 2.25" OAL limit ....
Ideally, getting actual .45-75 brass would be very nice. However, as far as I am aware, Jamison is still the only manufacturer currently set up to do them, and they are apparently still tied up with their government contract .... Mind you, it has been reported on the British Militaria Forums (by the moderator, who set up a group buy through Ten-X Ammunition, of Jamison-made .577 Snider and .577/.450 Martini Henry cases) that he gathers from his ongoing contact with Ten-X that they were rather fed up with some quality control issues at Jamison, as well as the supply problems arising from the government contract, and are turning to some other manufacturer for future case production. Since Ten-X manufactures loaded .45-75 ammo (in both smokeless and black powder loadings, and both .458" and .456" bullet diameters, I see) perhaps we could try to find out from them if they have another source for .45-75 brass.
Unfortunately, I suspect that it is not an option for us to try to get loaded ammunition from Ten-X shipped to us in Canada ... otherwise we could "bite the bullet" and buy some, in order to have the cases for re-loading.
I wonder if any of our U.S. pards who shoot .45-75, but don't load their own, would be willing to sell us their once-fired cases??