Jonathan, thanks for the quick reply, I need to learn to type faster!

I'm surprised that No.1 would be the better option. May I ask why that is?

If the screw has been turned down by that stage then would a shaft collar be sufficient for keeping it in place?

Edited to add: and again with the fast reply! The single hole on one side was the original design idea, just like the other blocks I'd seen. The reason for trying to a different approach was because I thought they were using standard radial bearing in the block and thrust bearings on either side, and using the angular bearings would benefit from a different approach. Clearly not!