The 1860 was indeed a cap and ball design. It makes sense that the nipple relief would be on the right side. The gun could remain in the stronghand while decapping/capping.

Tha model P was a huge military contract for Colt. The minor design cganges that you mention wouldn't have been an issue. If not for the military contract, the model P most likely wouldn't have come into existance.

You may not want to accept the fact that the SAA is a left handed gun, but it is a historical fact.