Where did my air suspension disappear to?

So, I got a really good deal on a 99 Expedition, 5.4, towing package, 2wd, 204K miles, 2nd owner bought used from dealer lot at 31K, ALL service records by the book. Drove it about 30 miles and parked for three days in my driveway. Went to start it at 0'dark-thirty one morning and would turn engine over, but no start. Had a friend that's a Ford mechanic check it and fuel pump has gone away. In looking for replacement I notice that the assm. are different for models w/ and w/o air susp. Since there is nothing wrong w/ the sending unit I puchased the kit that reuses the p/u assm. and only has a new pump and strainer. After reading the owners manual, I see the warning about turning off the air susp. switch before jacking, so I find the switch and turn it off. Get the thing up and on stands all around and I see a set of normal coil springs in the rear, the rear shocks look normal, no air lines going to or from them, the ride height indicator is in place attached to the track bar. I notice the words AIR SUSP molded into the rear of the fuel tank. Sliding to the front, I see normal coil springs, a set of normal looking shocks, except that at the top of each one there is a tee type connection on the exposed part of the stud with a line or cable going to it and then on to the spindle area and backing plate which I'm assuming is a wheel speed sensor for the ABS. AIR SUSP warning light has never been on. There is a unit in the right frt of the engine compartment, between the washer reservoir and rad support that looks like the top of what could be an air compressor.
Since I don't know what to look for, as far as orig. stuff goes, has someone already done me a huge favor and converted this thing to conv. suspension in it's early (pre-31K miles) life. Guy I got it from never had it done. It's time for shocks, do I just get shocks for non-air susp. model?
Thanks in advance for any insight.

Maybe the original owner traded it because it had suspension problems.