Andy, as far as I know (although I could be wrong, as I'm not 100% sure), the proper 'holed' version of the Melz is only available as 6H8C (6SN7), not as 6H9C (6SL7), which is what you need for your Croft.
The desirable 'holed' 6H8C look like this (I have some, which I use in my Copper amp):
https://www.ebay.com/itm/2x-6N8S-6H8...wAAOSw-RlfsdZA
As opposed to the 'holes' in Melz 6H9C, which are quite different:
https://www.ebay.com/itm/NEW-METAL-B...8AAOSwnHZYeuAO
You'll see that the construction of the (holed) anodes there is very different from those in the 6H8Cs, so bear that in mind:)
Marco.