I don't own a 45 Long Colt so can't help with a recipe..have done one and two ball loads in .44 mag for T/Contender.
I added the weight of both round balls and IIRC it came to about 246 grains total.. then used Lower than Start data for a single 265 grain bullet and worked my way up. Did the same for two and three ball loads in .444 and 45/70 and as long as you start low and work up it should get you what you want.