double, I'm happy for your success with the 1/3 HP motor.
I want to add a comment/caution about the 6 X 48 sanders. My old Sears sander does not have a removable platten like the Rockwell so running slower and on the lower end power wise is perhaps a way to ensure a longer life for the cast platten. Moving the work around, back and forth across the belt as well as up and down the length of the sanding surface, will keep heat and wear to a minimum. Over the years of reconditioning power tools I have had 5 of the Rockwell sanders (I have one to rebuild now, this one will stay in my shop when I get it done)none of them came to me with a motor but all of them did have a common condition - the plattens were seriously worn. They had hollowed out spots (wear depressions) near the work rest. I suspect they were abused by someone holding the work in one spot, pushing too hard, for too long with enough motor power to allow this to continue until it caused the dips in the platten. Quite possibly they were used for production deburring. Maybe unskilled labor interested in numbers of parts done and could care less about the proper care of the machine (speculation on my part). Getting anything close to square is impossible with such a condition. So not having a way to regrind them (at least 1 was too far gone for a regrind) I replaced them. IIRC @ about $109.00 each in ~1980. I'm almost afraid to see what a platten will cost today for the sander I want to rebuild. Somebody on this forum just bought himself a blanchard grinder, maybe he could use this one I have for practice - hint, hint. Another thing about it is that once you wear the platten (scooping out depressions) the belt stretches at these locations making belt tracking more difficult and the outcome from this is the belt wandering off and cutting through the sheetmetal side cover (if so equiped) or the aluminum cap cover I have repaired a few of these too.
Treat her right and she will last a long time, enjoy your sanding.