Mike, I e-mailed them with the question. Here is a link to Slimline. http://www.slimlineproducts.com/onli...rted_pitts.htm
They also have an inverted pitts muffler, for more money. I e-mailed them with the same question.

Hey, here's another one, with the dimension. Part no. BCMIOS91 , http://www.justengines.unseen.org/silsbcmdims.htm. It's 25mm deep. When I get home, I'll measure the distance from the centerline of the engine head to the face of the exhaust flange. This may work! I'll look for a U.S. distributor. Check back later. Rich