My 20 year old car now has now been registered. The process is complicated (too many documents) and therefore error prone but everyone involved in the process was very helpful. It took an elapse time of 2 months! I took the DIY route because of the age of the car and need to find competent technical people.
I have learnt a lot and I am not sure a gestoria could have helped.
The main problem with old cars is lack of familiarity with the type and lack of spares (eg headlamp glasses). The pre-ITV check did not throw up any problems but should have. It is a lot easier to buy a new car than import one!