The motors used to power these little vans which originally had a 72 volt system based on lead acid cells. What this means is that I could actually keep to 72 (or 75) volts nominal as with the motorcycle and keep using the chargers and controllers that I've used to. Testing with 96-99 volts nominal would be interesting, but would also require investing in a much more expensive controller. I'm also not sure if raising the voltage would give me any more useful power out of these old motors. Their useful powerband ends after 2000 rpm as you can see from the graph below.
Another aspect of these motors is their size. They're said to be 50-60 cm long which may or may not be a problem. Luckily my car of choice is not too small and the original engine is not very small either. Looking at the pictures I've taken I think I'll be alright. There's one measurement I should have taken that I didn't, but as I'm about 250 km away from the car at the moment I'll just have to wing it.