Possible to clean up or repair raspy/gravelly voice?

It's effectively distortion, and there's no real cure for that because you don't have a 'clean' reference to go by. That said, I fed your clip into Adobe's Enhance Speech tool (which you can find here although you should note that there are restrictions on how much you can use it) and this improves it somewhat by using an AI model to reshape the speech. As I said, not perfect by almost certainly the best on offer, certainly for free. I've attached the processed file.