I have a crank like that... And failing the possiblity of attaching the correct size to the inside of that chainring (and changing your chainline), the only option for change seems to be bottom bracket/crankset replacement... In your case, if you have a square taper, you could probably just do the crankset.

I've got a 52t on my front, and its just fine, wear wise. Its a steel cottered crankset from the early 70s, and is holding up amazingly well.

peace,
sam