Is an R3 block with a 50mm cam tunnel limited to roller cam bearings.

Just measure one of the cam bores...... that’ll tell you which cam bearings it takes.

Seems like there were a lot of different cam bearing options for those blocks.

My R-3 has babbits. they can be bored for roller. I think the preference is to bore them to a 60mm w rollers. There's better choice of cam cores at a reasonable price .

The owner of the block says it’s a 50mm cam bore. I want to built a street engine so I don’t want roller cam bearings. Was there a 60mm Babbitt option.

I seem to think there are 50mm babbit and roller options.
As well as 55 and 60, if theres enough meat in the cam tunnel.

There cam be issues with lifter oiling when the cam cores get bigger.

All 50mm cam tunnel R3 blocks were for roller bearings, from memory there is a durabond babbit bearing for a 55mm camshaft that fits the tunnel. There was an odd babbit size (largest cam journal on a factory camshaft, 1.998" I think), but I think they were the earlier R1 or R2 stuff