Yup, I recollect they (9mm Blackhawk cylinders) will physically fit, but should be fit to the gun so's the timing, gap, etc will work safely.
Ruger used to sell .45 ACP cylinders & 9mm cylinders & fit 'em to Blackhawks for $100+.
But no more. AND THEY
WILL NOT DO IT FOR A VAQUERO. Well, not for me, anyhoo.
MG