Having looked into this, generally a "professional conversion" refers to a company that is able to issue a new "Certificate of Origin" (or similar). In Georgia, this company must be registered much like a car dealership (and, in fact, uses the same forms). The new Certificate will usually list the original VIN, original date of manufacture, and the previously "finished bodywork builder" will now be something akin to an "intermediate manufacturer". The new "finished bodywork builder" will be the company issuing the new Certificate. Sound complicated enough?
That said, the company in question could (in theory, at least) inspect the finished vehicle, sign off and issue the new Certificate. The previous title *MUST* accompany this to the title office (and whatever other paperwork I am forgetting at the moment).