As the guy who coined the term 616 as applied to your 327 stainless creation, I must admit that I too am looking at adding a second cylinder to my project gun, but I’m thinking 32-20 rather than your wildcat 321 GNR... which I actually had never heard of.

As steelslaver mentions, the Model 53 cylinder may be a challenge because you would have to shave length off of a Model 53 cylinder to fit it into your gun, or shave the barrel tenon which would make it unusable as a 327. I’m not sure I would want to use the 53 cylinder in this way. Maybe it would be more economical to obtain another 617 or 648 cylinder to bore to 321 GNR or build another whole gun around the longer cylinder if you need the length.

Regards,
Froggie