molochmaster, What is the rear drop out spacing? If 126 mm you can use a modern 130 mm rear hub. If 120 mm you may need to respace the drop outs. I take it the RD hanger, fender and rack eyelets haven't been hacked off?

I don't know of a 26-48 equpped crankset off hand, but I suggest substituting a mountain triple w/22-32-42/44 chain rings (may want to change to a mountain FD). Square taper BBs and cranksets are still readily available for 68 mm English threaded BB shells.

Brad