I'm currently nearing (I hope) then end of a GTT build. The only figure I have is front & rear track is 1592mm. Unfortunately my car is away at the trimmers so can't measure anything for you at the moment - maybe someone else can.
Yes the chassis is still being produced, Chris @Vortex could update you.
Alternatively a little while back there was an unfinished build at the rolling chassis stage that someone was selling - I can find out if it's still available if you think it might be of interest.
As far as other build details, have a browse of their website if you haven't already :
My engine/gearbox is from a Ford Focus 2.0 Ecoboost. Brakes are Rover/Granada, getting harder to source but I believe aftermarket may now be an option. There's also electric too.
Good luck with your build - a Dino was another I was tempted by.