I still have a '99 Crown vic prepped for Lemons. Haven't run in the last couple years though. It's hard to get people to pony up $800 or so per person to race when it's not a true 24 hours any more (the MI races at Gingerman stop for the night). And there are so many cars it's hard to even get in the race, then it's hard to get any clean track time. Plus all the cheaters.
It's fun, and competitive, but at the last race I got punted twice by NDBs (Non-Driving Bastards) and we got a black flag for some stupid BS near the end of the race, and they poured a beer on our dashboard which ended up frying our SCT chip (only thing the chip was for was shifting - OD lockout, 1st gear disabled). Car is ready to go again, just need to change the fluids, touch up the paint, replace a coil, a control arm, and the chip.
I've seen a Mark VIII at the races. They didn't get too far. It's hard to find a $500 one worth racing. And honestly, a mod motor is more reliable than any of the older motors you'll shove under the hood. The air ride would have to go, and then the tranny is your weak link. The IRS is nice but I don't think you'll get any handling advantage out of it in a beater race - a couple whacks and you're way out of alignment, or worse. The Crown Vic was great because it was an ex cop car with jumbo coolers, solid axle, full frame - a tough car - and we just welded the cage to the frame. Ended up really nice and stiff. Handles nice, and the entire suspension is stock. Only "mods" were cutting out the cats and going with better pads and rotors.
Remember, reliability = 1 / the # of bolts you touch.