I don't know if the gaskets are different between a gas and a diesel but I do
know that there are three thicknesses of diesel gasket.  If you check the
manual you will see that it tells you to look at the little tab of the gasket
that sticks out from under the head in the front.  It has some type of marking
(one, two or three small holes, I think) to tell you what thickness gasket you
should use for that particular motor.
Have fun and check with Ron at the Bus Depot as he might have a cheaper price
on the gasket ( think I paid $35 for a diesel gasket from the FLAPS).
Ken Wilford
John 3:16