The only issue with a three screw Blackhawk other than the necessity to load five instead of six would be the cylinder throats as already mentioned. Ruger's 45 Colt throats almost universally run undersized of their bores making for questionable accuracy with cast bullets. Doug Phillips (Cylinderhone on Facebook)can do a wonderful job of correcting your throats if the they need it. I had my Bisley in 45 done by him and have a 41 mag and 357 Max cylinder there right now being honed. Both were undersize of the bore. The 45 showed a marked improvement in grouping after honing. From 4" groups to 1.5-2" groups with cast bullets.

Congrats on finding a great gun.