Taylors originally was going to use the 45Colt for the Spencer to help make it appeal to CAS shooters......way back while it was still on the drawing board, i spoke with Tammy Loy and told her to consider the shorter Schofield round as a Spencer originally only held 7 rounds.....in 45 Colt, the action would only hold five to six rounds....and that would mean you'd generally have to load 4 or so rounds on the clock at a typical CAS match......that would have really limited it's appeal.
And no, you will not easily convert it to the Colt round, if at all.