10 x 1.75 to 10 x 2.5 Rear Drums

I have a 71 Demon 340 and it appears to have the oddball 10 x 1.75 rear drums. Does anyone know if the 10" backing plates are the same for the 1.75" and the 2.5" wide drums? I thought if they are the same, I would just buy all the guts to convert to the 2.5" wide drums since they are more common. Also want to convert to the LBP while I'm at it. Anyone know if this will work? I know I'll have to buy new, longer axles. I want to upgrade to Moser's anyway. Thanks.