I doubt it could get an age related plate now... If DVLA asked for evidence of the 3.0 in a Beta I think that would need some creative photoshopping. Or finding a Pic of the rear engined Busso powered Lancia Beta that Mick Covill built and photoshop that number plate. Suspect this one will end up as either a trackday toy or go through an IVA test with a Q plate being issued. Unless you have an Alfa 164 donor car you could swap the engine number onto? It's a tangled web we (try to) weave.
Guy