The best way is to pull the bearings and get the number and measurements. The bearing numbers may be on the Vintage Machinery wiki site info. I normally use Accurate Bearing. They cater to the OWWM.org members, and Lynn is very knowledgeable. If you are not a member of those two sites, you should join. Once you are signed up you can navigate between the two easily. There is a wealth of info on the Vintage site and tons of help of the OWWM site. Be aware the OWWM,org site is strictly run by the owner and moderators, so read and follow the rules.
If your lathe is very old be sure to check the wiring. When changing the wiring on my friend's over from 220v to 110v most of the insulation crumbled when touched or moved. You will need 14-3 for the feed and switch if you are going to run 110v, and 14-4 for the switch if you are going to run 220v. I would run 14-v 4 for the switch so matter and not switch the neutral if running 110v.
BTW, the belts are "A", or 1/2" belts.
St. Louis, MO
Retired Welding Inspector and past Ind Arts teacher