Out of morbid curiosity I asked one of these conversion specialists in South Australia. As it turned out he knew and loved the P6B and advised as a minimum $125k but likely closer to $150k.Yes I would be very interested. There are a number of companies in Australia already doing this. Why Australians Are Converting Classic Holdens Into EVs. But according to this article it is very very expensive to get the regulatory approval. Over here to get a "HQ" Holden done, think of a larger FE Victor, is $60,000 or 30,000 GBP.
Ouch. This would have to be very much heart over head. However if it's a DIY job it may be cheaper. If it's your passion, give it a go.
Lewis