My '57 GH Setup had a bad idler pully bearing. It had been sitting a long time and just froze
 up and was rough when you spun it. This pully consists of 2 steel halves sandwiched together
 and riveted.  The bearing is in the center. I tried to find a new pully, or match one up, but
 didn't like any I found. There was one pully available from the tractor supply, but the center
 hole was too small.  With nothing to lose, I decided I'd drill the rivets out and see if the
 bearing could be replaced.  
I put the pully on my drill press- and carefully removed the head of each rivet. Then I punched
 them out. The bearing and center "post" came right out. I drove the post out of the bearing 
(it wasn't very tight), cleaned it, and looked for a part number. The bearing is a New 
Departure #8503. Even though ND isn't around anymore- the #8503 is still a good reference 
number. My bearing supply ordered me 2 new bearings (I wanted an extra).. and they came in
 yesterday.

It was very easy to repack the bearing with grease, and sandwich it between the 2 halves of 
the pully. I used (6) 1/4-20 x 1/2" SS Bolts, nuts and star washers (locktite too).  Now I 
have a "new" pully....

Ray