Thanks for the replies hwtyger and Geezer.
As we have already found there were 54s made in .25 albeit that I cannot see that many were produced as demand was likely to have been low. Due to this I don't think this is an option anymore on the 54/56 series guns though in the former case I'm sure it was a possible option up until a year or two back.
I think the combination of the gun's heft and less popular calibre makes this gun a little more unusual than most.
I'm greatly enjoying it's quirky-ness. But I have no doubt at all this is a serious bit of kit in a hunting set up.
Not quite sure how a lightened piston set up would work with one of these as its a big ole lump of lead thats being pushed up the barrel.
But If it works I would imagine that type of conversion would be absolutely awesome.
Dave