Prarie boy - Yes this die would fit your press. It is the standard 7/8" thread. But I'm just wondering why you want to buy one for your 45-70. I am sure the dies you are using now have a roll crimp die which is good for this cartridge.
The Lee factory crimp die is a good die and I use them in my .223, .270 and 30-06 (and for my 300WM when I had one) and this die works great for these bottle neck cases. The reasoning is that it provides a more uniform tension on the case mouth/bullet interface resulting in an increase in accuracy.
I've found that my accuracy has improved in each cartridge from only a little to a significant improvement. But personally I would try the crimp in your existing die.