The spirit box dwell control feeds the reverb signal back in the pt2399 chip. So it still uses the 6 pin.
the 10 pin is quite nice, I’ve mentioned the 1776 rub-a-dub reverb deluxe as a nice simple iteration of the 10pin in other threads, and I think the reverb sound is smoother compared to the Rub-a-dub I built using the 6 pin. You could do something with that, but since the 10pin needs a dual pot for the dwell, you’d need a DpDt momentary stomp switch. So that’s an option too. In my experience, the rub-a-dub deluxe can get long reverb, not as long as the sparialist cavern patch though, so I’m not sure if it’d be enough for you. I haven’t built a ghost echo so I’m not sure how much Max dwell that gives either.