I've heard bad things in terms of installation, but I've seen pretty good dyno results on otherwise mild 302s. It would probably perform well with your setup. Also, whatever you heard about it only "lining up" with stock heads doesn't make any sense, because any 302/351 head, stock or aftermarket, has the bolts and ports in the same place (extreme application race parts excluded). Its the same reason why we can choose to go so many different routes with our engine combinations. If it works on a stock head, I'm sure it will work with the GT40s.
Like RiceSlayer302, er, I mean, 5.SLOW said, I also have a friend who has one and likes it. I myself don't have a lot of confidence in
BBK products, but that's just me. I definitely give it props for looking different.