Vacman117
I had an Oreck U4120H2B Manufactured in 2007, which had the "Johnson" brand motor in it w/ the standard flat belt drive shaft.
I purchased a used & beat-up Oreck U2000RB-1 off of eBay, which also had a "Johnson" brand motor in it - but this one had the Grooved drive shaft for use w/ the ribbed Endurolife serpentine belts.
I had originally planned to do a direct motor swap from the U2000 into my U4120, but the U2000 motor looked like it had been to hell and back - like the previous owner had likely vacuumed up water at some point. - The motor still worked, but the bearings were completely shot.
So, instead of doing a direct motor swap, I decided that since both motors were IDENTICAL with the exception of the drive shaft - that I would keep the field assy. from my U4120, then transplant the U2000 armature assy. w/ grooved drive pulley into my existing motor, after of course, replacing the armature bearings with two brand-new SKF 608-2RSJEM C3 bearings.
After performing "transplant surgery" on my U4120H2B motor & reassembling it with an armature core from the U2000RB-1 donor motor -- everything went back together without issue... except for my struggle trying to figure out how to get the Endurolife belt on... but once I got the Endurolife belt on (thanks to VacuumLand), my "frankensteined" Endurolife Belt Oreck U4120H2B roared happily to life & is quite honestly running better than it ever has before during my ownership of the vacuum!
Vacman117, unfortunately I don't have any of the older "Classic" style Orecks in my collection, so I can't ascertain whether or not a newer Oreck motor would be a direct fit for your older-style Oreck Housing. - You would have to ask another VacuumLand member who has more experience than I do with the older Oreck machines.
Best of Luck to You!
~Justin in Chicago