Loads of threads on replacement MFT tops and the various jigs available. I researched them all, costed them all, visited CNC Design in Wrexham as I live reasonably close and came away with two Medite MDF tops ( one standard, one custom sized whilst I waited) and would never ever contemplate making my own.
Fully agree with Marineboy's comments. Absolute quality, total accuracy and half the price of the original even without the turned aluminium dogs which are supplied gratis.
It all boils down to wether you want to purchase, size and then bore your own top. But MDF, dogs and jigs (had a very close look the Parf jig in Axminster Tools.....superb engineering and design) are not cheap. Factor in your time, a workshop full of dust, replacement cutters and a set of dogs and it was a no-brainier for me.