The camera height position will always cause debate.
GSV cars are set at 2.5m, yet Google recommend 1.65m indoors. I believe most Mapillary driving captures are made at dashboard/windscreen height, so even lower.
We are all used to the GSV car camera height because we’ve been using it for a long time, but I, like @OmniSynThesis360VR feel that to get a real persons perspective mounting the camera as close to eye height gives the best view.
It also depends on the usage case intended for the captures. I’ve made some public transport access captures aimed at people who need disabled access and for people with autism. Making captures with the camera mounted at 2.5m is not ideal. I’ve even made a virtual tour aimed at small children and the camera was set at around 0.9m high.
Many trails I’ve captured I have to mount the camera just above my head anyway to minimise getting caught up in low overhanging branches. I simply wouldn’t be able to walk many sections with the camera set at 2.5m up in the air.
Apologies for going off topic.
As for a car mount, I’ve made my own. Our car has an electric sliding sunroof and I’ve made a wooden adapter plate that I can clamp into the opening in combination with a height adjustable monopod, the base sits in the armrest inside the car. It works very well, but is very much s bespoke solution.