WOW you got an 1875?! Now that is a classic!
For pretty much 75-78 I think the forks are all the same. If you change out the forks, best to do them with the lowers though as at some time, the innards changed for connecting the lowers and forks.
As for modern forks, the 69-78 use 35MM diameter forks so you would either need 35mm replacements or the whole front assembly including the triple tree and stems. Them you will probably need custom bearings.
The ride IS the adventure. The destination is just to get gas!