Martyn
My Stuart Beam has split main beam bearings and it is at least 30-40 years old. I got it part built 25+ years ago. The drawings (parts, #90048 and GA, #90047) that came with it show split bearings held together with hex cap screws. I have changed them to studs and nuts to be more prototypical as Jeff says. Perhaps the solid ones in the picture are replacements for ones that got lost, or didn't bother splitting them ( or for non rectifiable mistakes during machining?).
John
edit: Jason beat me to it!
Edited By John Purdy on 25/01/2021 18:26:47