when you took the cover off the part that the cable hooks to did you see 4 bolts or screws in there. mine is a gas and a little different, if there are bolts or screws , that's how it is removed. I'm pretty sure that part comes off and I would take it off first then remove the tach drive so you don't damage the gears. I don't think theres a gasket between the pump and block.  you  can call maibach tractor 800-808-9934 or korves oliver  618-939-6681 for gaskets and any parts you may need, they are very helpful for any questions about your project. chuck