Scott
I am assuming you are refering to the front induction rear exaust ABC engine from a few years back. I think I know of a source for the information you are looking for. You might give a call to Performance Specialties and ask for Dave Shadel. Dave in the past was probably the formost expert on the ST x-40 on this side of the Atlantic. He built them for Formula-1 racing, when they were no longer available he moved over to the Nelson engines. I new Dave back then and he is a very nice person and should be able to answer your question.
Andy Borgogna