I don't really care about detracting from the value. What I do think the louvers will do is detract from how special your car really is.

How many 383 cars got Shakers?

And it's an FM3 car too?

Those two items are HEAVY! Adding louvers is like adding a lazy eye to Pam Anderson (or take your pick). It's your car and there's nothing wrong with adding something that you like, but your car sounds so special.

Have you added anything else to the car? Rallyes? Your answer may help nudge you one way or another.