Sometimes rules are set by as much as what they don't say, as what they do say. In the rule book, both Gas and Altered are allowed engine set back, and as it spells out for them what it is, then because of the specific omission of a set back clause in GT, it might be said that it cannot be allowed simply because they don't say that it can be allowed.
To further confuse the issue, in Modified Sport, which is the next step up for sport cars from GT, it says that engine placement is optional. So I would read that as set back is a non-issue. Even in Altered the rules are more strict than in Modified Sport for set back.
The way I read it, you cannot set back the engine in GT. But that still does not take care of the placement of the engine in engine bay itself.
Far be it from me to say what it should be. I am not on the rules committee nor am I on the technical committee.
The problem for me, is that I don't live anywhere near anyone who has built a car to the rule book. And I don't want to put a lot of time and effort into something that will not pass tech inspection.
I have emailed the SCTA tech committee a few questions and have received answers. Maybe that is an avenue you can use.
I think there has to be a certain amount of ambiguity or the rules book would turn into a rules encyclopedia. Although it can be hard to build something substantive out of someones interpretation of a rule, especially if there is more than one interpretation of that rule.