ok so I took my own advice, and started from the other end. Have not done enough track work, of late :D
But to get the minimum 36" radius (915mm) I had to cross some dense foam. So I used the sanvic file to level out the foam and glued the foam in place after marking its position in texta. After attaching foam, I relaid the track, and glued it to the foam as I was unable to tack it down.
A bit of weight and see tomorrow if it is level and stuck fast.
The 36 inch (915mm) radius looks ok. The space between the tracks should scenic up nicely.