The Winchester 54 was pretty much a sporter version of the Model 1903 Springfield, not the Mauser, and it has the same cone breech as the Model 1903 and the later Model 70.
The .30-30 is rare, but the rarest calibers are 7.65 Mauser and the 9x57 Mauser. Both the Mauser calibers appear to have been made with the export market in mind. The gun itself is rather rare, only some 50,000 were made before the 54 was dropped in favor of the Model 70 in 1936. The guns have a lot in common, but I don't know what parts (if any) will interchange.
The main complaint on the 54 was that with its stamped trigger guard, it looked cheap; the Model 70 corrected that, and also had a better stock.
Jim