You certainly can put more underbody covering on the car. Check this link:
http://www.pro-touring.com/forum/sho...ight=belly+pan
He had pics at one point but my computer dopes not seem to be loading them now? If they don't come up for anybody else, I have copies that I dl'd to my hard drive.
The thing is, only the very rear of the driveshaft moves. The front of course remains stationary. If you really want to leave the driveshaft exposed, find some driveshaft loops (drag race safety equipment and good insurance in case you ever lose a front u-joint) and use those as mounts for a smooth panel on either side of the driveshaft.
I'm not sure if the Lincoln uses a 4-link rear or leaf springs (I'm not a Ford guy) but either way you could probably do some aero around the rear axle using a sheet of flexible plastic. I'm working on this for my LeBaron (FWD, but a solid rear axle) and I think if it was attached to the suspension controll arms and the axle it would work fine. The plastic would be able to flex with the movement of the suspension and hopefully wouldn't make the kind of sounds you get from flexing a large sheet of metal.
For the rear of the car, looks like you could benefit from vortex generators or a lip spoiler. If you can, grab the March issue of "Hot Rod" and read the wind tunnel article they have. Talks a bit about lip spoliers and how they can be used to reduce drag. Basically tricks the air into thinking you have a boattail.
See if you can find more aero mirrors. I'm sure yours look alot like the ones on my '70 Caddy - very square and brick-like...
Consider an extractor vent on the hood like Ford used on the GT-40 (try google images if you are not familiar with it). It can help redirect what air does need to come into the engine bay back out and avoid it going under the car, plus it can help 'fill in' the low pressure/detached air flow area you likely have above the front of the nose.