the 924S, 968 and 944 are all the same chassis and the swap can be done with the same parts. The 928 is a factory v8. Could have been one with an exhaust, although they sound more like a bmw/lexus v8. I would like to put an ls1 in mine, thats for sure!
Was it this body style? I will admit the 924 does look like an rx7, esp from the back quarter(although it came out first)