I’ve shot with owners of .45 convertible Black Hawks (BHs) that were machined to also fire .45 AR. If I owned a large frame .45 BH I’d have the ACP cylinder modified because I reload .45 AR and the only disadvantage I can think of would be possible loss of collector value which isn’t an issue with most new model BHs.
For the dimension the O.P. wants why not visit the Small Arms and Ammunition Manufactures Institute (SAAMI) and get min. & Max. .45 AR head space specifications. The rest would be feller gauge measurements and arithmetic. SAAMI