Confirmed, the existing mirror housings can be reused. Here is the new V6 Exige mirror plinth. It comes from Lotus with both halves bonded together and with the ajustement and bellows attached.
Part numbers are A138U4013F for the left side and A138U4014F for the right side. Total, including shipping from Deroure was about £75.
Separating the mirror from the housing was a bit of a pain. It took a lot of patience, but I was able to get them apart without scratching the paint.
I included a picture of the existing mirror housing after disassembly. Once the push on star washer is pried off, the whole adjustment assembly comes apart.
The outer mirror housing is held onto the new plinth with the spring. Once I determine paint/coating on the plinth, they will just slide together and be held in place with the spring.