Dual exhaust was an option on the Marquis's. The factory system used an H-pipe that bolts directly to your existing converters. From there the dual mufflers and tail-pipe mounting points are all there, if it had duals or not. You will need the appropriate hangers and brackets for the driver's side exhaust. (Since the passenger side is the same on both single and dual cars all those hangers are already there.) All the parts are identical between the Crown Vic, and the Grand Marquis....so parts are pretty easy to get. Any exhaust shop can do it easy enough....the only question might be if you have strict emission laws where you live, they may not want to change from stock.
After-market mufflers will give you a much better sound over stock, and flow better too. I went with DynoMax Super Turbos, and mine sounds like a Mustang GT at idle, with a very sweet tone as you accelerate. The choice in mufflers really comes down to personal preference.....sound, price, warranty, etc.
My custom side-exitting system ran me about $325 total.
1993 Grand Marquis w/170,000+ miles and counting. Now it's time to make her FAST!!!
12" conical K&N filter, Custom side exit exhaust with X-pipe and Dynomax Super Turbo mufflers, replaced stock fan and clutch with PI electric fan and PSM fan controller, Aluminum PI driveshaft.
Body mods include a '95 Cobra rear spoiler, tinted windows, 17" Mustang Split 5-spoke rims w/ P255/50-17 BFG g-Froce TA radials, and a 14,000lb Auxillary Trans Cooler.
Interior: Custom A-pillar guage pod w/ Digital oil pressure and Trans. Temp. guages.