Bore Gauge Help

Hi, Have a block here that I need to check out for wear etc.

1. Once the rigde is cleaned, this will give me the original bore diameter - correct?

2. Measure just below the ridge where the rings meet will give me the bore diameter plus bore wear - correct?

The motor I am looking at I hoping just to at most re-ring. This will be temporary while I have another rebuilt.....What is the maximum wear I can get away with, before a rebore is needed?

Any other useful tips would be welcome - TIA!