I've never heard of a 90 adapter for this application.
Sorry,but it sounds like you'll need to modify the exhaust.

Just how tight is it?
At first I wondered if you could 'dimple' the pipe but if it's that close,heat might also be an issue.


1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.