When we bought our scooby, we got the RAC to do the inspection on it. Altho they couldnt say about the mods, they are able to tell you if there are any faults or problems with any part of the car. I was really impressed with the RAC check, they picked up on a few very very minor things that didnt bother me, and I would never have noticed.
It was expensive to get it done, but it was piece of mind knowing everything was ok and in good condition.