The 40-65 WCF is a longer 45-70 length cartridge. The toggle action used in the early Winchesters if scaled up for a 45-70 length cartridge would have made a very large heavy action. The old carrier design used in them had to be totally in front on the toggles, so the extra length of any cartridge needed the receiver lengthened about double that. The Bullard's for 45-70 length cartridges, which used the same carrier design, have a very long action.

The original cartridges for the Model 1876 Winchester all had the same diameter rim so all the action and magazine parts were the same. Later 45-60 cases have a slightly smaller rim the same as a 45-70 which is probably the base case they were made from. 

According to 'Old Cartridges of the World' the 40-65 WCF, 40-60 Marlin, 40-70 Bullard and 40-75 Bullard all would interchange.

I  have seen that in a lot of cartridges, first in 25-20 SS when I acquired my first rifle with that cartridge using large primers.