I edited my post to reflect this. I should have gone back and re-read the entire post - forgot you were going to use the .45/90 case. Still an excellent choice.

Steyr data should be useable, but start at Hornady's starting loads and go from there as pressure indicates. As in the .376 Steyr and my .375/06IMP, BLC2 and H4895 wil be very good powders for it.