50Cal,
The Sharps base, rim, and rim thickness are suitable but the .50-90 2 1/2 is too short.....the 500/450 No.1 express is a 2 3/4" case length.
As I mentioned a couple of posts above, the Sharps .50 3 1/4" will work, just lop off 1/2" and full length size.
Sharps rim is nominally .065" thick while the 500/450 No.1 is ~.060" thick. No issue in my Cogswell & Harrison.

With a modern chamber neck reaming might be necessary, the chambers on antique originals tend to be "generous" in their proportions.......I'm guessing it was to accomodate the early rolled brass cases which were pretty thick neck diameter wise.
- Mike