ORAC, the Bawdsey bunker is in a very sorry state now. Yes, the R4 were the bigguns, having three levels. The one on Bawburgh Road Norwich is still intact and was extended with an additional level. I think the Easingwold one was to that design also and was extended by adding another level on top, but it leaked like a sieve. Kelvedon hatch can be visited in essex and is signposted 'Secret bunker' from the A12.
The bigger ones were intended as Sector Ops Rooms, but were soon redundant thanks to the kelvin Hughes projector, which made it possible to read the radar imagery and control the fighters from one site. Combined with much improved radar performance and effectiveness over greater ranges, the majority of Rotor installations were obsolete as quickly as they were built. Quite handy really, as there was never the manpower to operate the full Rotor system 24/7.