After some experimenting, I found that a green LED and a Radio Shack photocell work pretty well. I used the smallest photocell in the pack that RS sells. The smallest photocell offers the most dark resistance, about 400k. I made a bug with shrink wrap tubing.
I may try a Vactec Valtrol sometime but I like the way this is working.
I'm building the cabinet now. I found some SUNN tolex and corners on eBay. I still need similar grill cloth, handle, and a nameplate. I'm trying to get this as close to original as possible but it won't be exact.
Also, I found that the Gibbs reverb used in 60s Fender solid state reverb units and Hammond organs has the same "1122" marking as in the Solarus I have to compare to. Those are fairly readily available on eBay. This may be helpful to anyone trying to fix their reverb.