I own a large frame H&A that I rebarreled to 50-70 I had to make a new extractor and silver soldered the barrel shank into the receiver. I also have a Merlin & Hulbert small frame in 22 rf that is nearly the same as a H&A m 922.
I have rarely seen a medium frame for sale and the ones I have seen have been in poor condition. Being your rifle has been modified and not really a collector gun I would see if you could get someone to just fit a used take off barrel for it as all you would be loosing is the barrel markings and would have a lot less money in it. I would probably make it a 32 S&W long or maybe a 32 H&R as you can use about any 30-32 cal barrel and they are a dime a dozen used.
Just my 2 cents.
Jedman