If you want to put something in the space between the roof panels, I'd use something inert like silicone sealant. There are just too many horror stories about spray foam. I would never dream of using it in a vehicle.

You might want to check out this thread:

http://67-72chevytrucks.com/vboard/showthread.php?t=440440


1960 GMC 1/2-Ton Pickup Truck
In the Gallery
Updates in the DITY Gallery
Now cruising in the Passing Lane