Well Slim, you have a very interesting project.A few comments:
1. Conversion to 44-40 can be done in that cylinder, no problem. Plenty strong enough, plenty of length and plenty of 'meat'. It was in fact a factory caliber on the 1st model Hand Ejector but scarce.
2. You already stated that you intend to use only 44 Spl in it and that's the right decision.
3. your gun does not look buffed so thinking the markings are buffed off except for logo and proofs in actuality is because there were no other frame markings, i.e., the right side address and/or 'Made in USA' was not introduce until years after your gun was made.
4. 44 Mag 4" barrels are fairly desirable so a sale of your bar & cyl or trade for another caliber (more matching the vintage of the frame like a barrel w/o rib) is very do-able.
5. If you decide to keep it as is, I'd blue the frame to match.
6. I notice the front sideplate screw that retains the cylinder yoke is a torx head screw. It must have been the only one someone could find to replace the original. But there's lot'sa sources for correct screws.
7. I presume you meant a 586; 588 is nonexistent.
What is stamped on the butt, just the serial #?
Let us know what you decide to do with it.