There's about 7 fox body mustangs in my area ranging from beater to very nice clean daily driver. All of them have V8s and fly down the road, no one's fooling me with one lol. Still I get what you guys are saying, the base model is a 4 cylinder so badged as one it would make for a good sleeper I agree.
Just to be clear there is no car or year restriction, this is a "sleeper theme". The guild lines are that the cars must not appear to be fast. Whether it's a rusty crusty classic or a newer plain Jane 4 door sedan. Let's face it the go to 2 door muscle cars like Chargers, Camaros, GTOs, Mustangs etc. from the late 60s - early 70's aren't really going to fool anyone anymore. I'm not saying you can't it's just it's becoming a more common build option in the 1:1 car world much like Rat Rods are. As Rob said earlier if you want to fool anyone with one it can be done but it's really got to look bad. It's still an option on my list of ideas, though I would be more interested in an early to mid 60's rusty crusty 4 Door or maybe a wagon if I can't find something else. Still browsing the odd ball cars, I'd really like to get my hands on a '90-ish Cavalier but all my searches come up short.