Is there any way 1500 Pistons will fit 1200 rods?
I see that the pins from 1500 Pistons are larger, but any bushes etc that help in conversion?

Not sure what you're after here, but the 83mm pistons from the 1500 motors (69x83) won't fit the 1200 40Hp engines.

However, if you want to get 83mm bore pistons onto the 40Hp these already exist without buggerising around with bushes and mismatched parts, see link below

http://aapistons.com/collections/vw-piston-liner-kits/products/83x64mm-1200cc...