Removing Motor Mounts from 81
 

I bought some new mounts for my 81 4.5 and mounted them to my engine. I went to my car to remove the 1/2 mounts (MM's broke in 2) still mounted on the crossmember(?), but I can't seem to remove the single bolt holding it on. I haven't gone under the car to look but did a quick feel to see if I could feel the bolt. Is there something else I will need to remove or loosen to get to this bolt holding the lower part of the mount?

The steering rack has to drop down to get to those bolts. The tie rods can stay but you'll need to slide the steering shaft input off and the 4 rack mounts. BTW, the steering shaft will have to have its bolt removed in order to slide, not just loosened.

So the best way to do this is to mount the Motor Mounts to the Steering rack, then lower the engine on them?

So, 4 rack bolts and the shaft bolt holding the steering shaft on. Correct? After this is done, remove old mounts and put new ones on. Then lower the engine onto the mounts and bolt up in this order?

Yes, that sounds correct although there might be a few more bolts on the crossmember bottom piece, they're easy and obvious though. The mount is held on by a single bolt to the crossmember but the steering rack is right there blocking it so it has to move.