Hi, i hassled them (in a nice way) to get registered as my insurance with osbornes and sons only lasted 2 weeks !!! from the date i started which included the sva test. I managed to get past sva in 1 week. failed on the thursday - booked for retest the next wednesday and thankfully passed. Went to DVLA on that friday and filled in lots of stuff and booked inspection for the next thursday (the chap only worked on thursday in the office at bristol) had to attach an extra chassis number as i only had a riveted plate which wasn't good enough, so i got a garage to inspect and stamp a form to say it had been done. Returned the form on the friday and then had to wait til the next wednesday to get the reg number. so all in it took 21 day/3 weeks from start of sva to on the road. thankfully the insurance had got my address wrong so i managed to wangle that extra week with no probs as i couldn't register without certificate. If you have your chassis number attached correctly and your insurance cert then you should be able to get it sooner.
the chap at bristol didn't really look at much and was stone faced and had little interest in the car, hope you get someone better. He checked the engine number and the chassis number and that was about it but asked about the axles etc being from the seirra.
I can't understand why vosa couldn't do a check at the sva test time to say that the car is new/age-related or Q plate so we don't have to pay a grumpy man at dvla with a torch to inspect my car for 5 mins. rant over
Hope that helps, feel free to ask if you need anything else.