I know there's a few kits out there, but the Strutmasters conversion kit is the first one that comes to mind, and it looks like you can still buy it new which is nice.
Find the Strutmasters 1993-1998 Lincoln Mark VIII (8) 4-Wheel Air Suspension Conversion Kit With Shocks (FG14F) (FG14F) with free shipping on qualifying items at Strutmasters, the home of the original suspension conversion kit. Upgrade your vehicle and save time and money buying and even...
www.strutmasters.com
I feel like I've seen inconsistencies with ride height post-conversion with some brands, so if you like what you have now, it's probably worth searching around to be sure you replace it with an identical kit.