Bearings for Revox reel to reel

I need to replace the bearings of a B77 / PR99 reel to reel tape recorder. Do you know what is the best type and brand of bearings for this tape recorder?
You might ask Jack Clark at JM Terchnical Arts in Nashville. He was Studer/Revox's US Service Manager.
Do you know if they are 606 bearings? Or something else?
They are not 606 - the 606 is 6x17x6mm and the PR99 ones are 6x19x6mm - it is the 626. Revox uses a standard quality type, but I read that some people replace it with low friction/low noise much better ones.