why don't you go for clean over sleeper? But if you must try sleeper, a few issues back in Sport Compact Car there was a GSX that did a custom 3" exhaust that exited in a stock appearing muffler...take a looksee, it may give you some ideas.
The issue was "Midnight Club" and it had a pic of the eclipse on the front getting ready to race a Vette
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Black 98 GST missing her owner and looking for a new one...Inquiries welcome