Chris,
Not to save the cost of a gasket. There is an earlier extensive discussion about the use of the big baffle plate here viewtopic.php?f=2&t=10757 . From that I put together another RD18 without the baffle. I used that a lot last summer and had no problems. That was the experience of others too. It is the same as the original setup on the 1955 RD17s. Not to revisit that long discussion but RD17s and RD18s have run fine with and without the baffle.
I would like not to replace the existing exhaust gasket if that is possible. Prefer not to deal with removal (asbestos) although in the past I always used new exhaust gaskets.
Appreciate the comments Chris and Dan.

Can anyone address the question of reusing the gasket?