If you were to stay with the analog servos, you'd need something like CS-Labs CSMIO/IP-A, Dynomotion K-flop with Kanalog, or there are Mesa boards that can handle it for LinuxCNC.

Have you got a photo of the turret?
I thought Denford only fitted either their own turret, or Barafuldi turrets.


Personally, I'd fit modern servos with step/dir control if I was to retrofit another cyclone.
Although I fitted new servos to mine (I opted for a 400W on the X, and 700W on the Z), I still ran them in Analog mode, as I wanted to use a Dynomotion Kanalog board for the extra IO it gave (their Konnect expansion board only came out after I'd done my retrofit).

For what I mostly turn now, I'd also consider a standalone controller. However I did like the the Mach3 turning wizards for quick programming when I first got my Cyclone running. Even after I moved to running KMotionCNC, I still kept a licensed copy of Mach3 on the computer for generating code, as it was handy for occasional simple parts, instead of dragging a laptop out to the workshop.