I have a slightly different problem. I have a basket case D Rapide which had (still has) a seized engine when I was given it in 1989, and had not been taxed since 1969. In 1989, the DVLC were not interested in my notification of a change of ownership until I could tell them it was roadworthy. I have all the original papers and have known the bike since 1956 when I was an occasional passenger. How do I decide if it counts as a vehicle of historic interest in anticipation of an ultimate rebuild with rusty parts replaced?
It's down to the description.
A rebuilt vehicle is when an owner starts with basically a complete bike which is then restored or rebuilt replacing rusty, worn serviceable parts as required. I.e. Engine internals, wheel rims, exhaust etc. As long as the identity has not changed in that it's the same engine, frame, gearbox, forks etc as it was 30 years ago then you are not a reconstructed vehicle.
A reconstructed vehicle is something that on owner has created within the last 30 years that may look correct but which is a collection of parts sourced from all over the place to create a vehicle. I.e. the classic story of "I started with a fuel cap and built this bike from what I could gather".
I suspect your series D falls into the first description. If your still not sure, then to cover yourself, subject the bike to a voluntary mot. This is after you gave got the bike ready for use on the road though.
Whether a vehicle is reconstructed or not only effects it's MOT exemption (or not) position. It has absolutely nothing to do with historic taxation class which is a separate matter completely.