Rock Auto has 3665606 in felpro brand for $2.86. But will be $9.00 shipping
https://www.rockauto.com/en/catalog/chevrolet,1950,truck,3.8l+235cid+l6,1487137,drivetrain,differential+gasket,13411
The fact Rock has them.......every parts chain storecan get the gasket from felpro.
Classic parts has the gasket but you will have to confirm they are for the 3600.......picture even shows the blue green color. It might be for the 3100.
http://www.classicparts.com/Rear-End-Parts/products/71/3/0
