Sometimes you just have to take off the covers and get out some tools and start measuring.
Vernier calipers are your friend.
Sometimes your lucky and can move things around a get some measurement without disemboweling everything.
Often even if you cant find the numbers on a bearing, a supplier can sort you out just from the measurements.
My ST 10 head had nothing written on the bearings.
All my Chinese genheads now have Timkin or NSK bearings, And I know they are far better then anything, China was going to install.
Best of Luck.