You're right, all cylinders start over 54mm.
As there is only 0.011mm across the production tollerance for all three cylinders you're going to need a very very accurate vernier gauge indeed to measure them like that.
I guess that's why the cost of veniers runs from about a fiver up to several hundred pounds.

What really matters though is not the overall size or the letter on the cylinder / piston but the clearance which as I mentioned somewhere recently should (according to the book) never be under 0.039mm and has a service limit of 0.1mm.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread