I have owned two .45-60WCF rifles. And all I could get was cut down .45/70 brass. I took a Lee .45/70 case trimmer and shortened it so I could reduce the size of the Government length brass to the .45/60 length. I did a batch of 100 the first time and 150 the second time. Can't remember how long it took, as I was concentrating on the process and daydreaming about how I was going to load them and what bullet, powder charge, and type of powder would be best.
Your best bet is to trim .45-70 back to .45-60WCF spec's.