The club I race at must be one of the last in the UK that still race foam tyres in most classes of racing.
We have found the Enetti Tyres to work well for us, 42shore front, 40 shore rear. Or if you can't get those, some guys use CONTACT foam tyres (distributed by Schumacher). Sorry if that's a swear word on this forum
A popular choice is 30mm rear tyre, 26mm front. (Although fitting 30mm rear can be a problem on the t4, you'll need wider hexes) 6mm tends to work.
As per above info, yes we run a front diff on a small track, I use 40,000 front oil, 3,000 rear.
Hope that helps