Your Denon SS-730 is indeed from the early 1970s and was a direct competitor of the then budget market leading Pioneer PL-12D.
IOW, it wasn't a bad entry level deck for its time, but, as was intimated above, would be seriously outclassed in a Naim separates system.
Have no fear running it into your Naim MM input though. That is, as long as the deck is working well and the tonearm moves freely, your Rega Carbon (itself a rebadged audio-technica budget model not too far removed from the AT95E) will let you enjoy your records well enough. That is, at least until such time as you decide whether or not you'd care to replace the Denon with the likes of a Rega RP3 (the minimum standard for use with your amp) or better.
In the meantime, I wouldn't recommend pursuing alternative cartridges, as the Denon doesn't warrant such.
Craig