I was gifted a Surefire Centurion today, it's a Non C or M but just marked Surefire Centurion Serial Number is A00034.  I know from experience they have crappy battery life and was thinking about boring out the body for 18650 batts as I've got a ton of those and two chargers already. I'd replace the p60 with a CREE LED which in itself does no harm it's the boring out the body for the larger battery that would be my concern.   Does an Early Centurion have any collectors value or is it just another old Surefire?

It likely has some additional collector value depending on its condition. Have you considered just buying a couple of 16650 cells? You can use your existing charger and new P60 without having to bore out the body. A 2200mah Sanyo cell should only cost around $8.

FPNI.

Don't mess with the factory body.  There's just no need to bore a light unless your drop in has such high amp draw requirements that you MUST use an 18650.