Jaguar S Type 3.0 litre

Who can help with this query - if I go onto the JEPC to buy main bearings for the above car .it refers to Grade 1,2 and 3 - each with a diff part number - What exactly are the grades standing for - is it the size of the bearing with grade 1 being standard size,2 being +10 and 3 being + 20 ?

You need to find and download my ENGINE COURSE 168 I had converted from my 3 ring binder Jaguar Training to .pdf.

It is ALL OVER the internet and Gus has it on his site. (jagrepair.com)

The bearing guide should be stamped on the side of the block.