Let's address the bushing material issue first. Polyurethane bushings have been on the market for some time as an alternative to factory rubber pieces. The advantage is that the urethane typically has a higher durometer than rubber-that's industry speak for the measure of stiffness of the bushing material. Stiffer bushings deflect less and should, in theory, improve the vehicle's handling characteristics by effectively tightening up the chassis. The effects are most noticeable during tight, high-load turns, particularly on turn-in-the point when you initially point the car into a turn-where chassis responsiveness will be sharper. Most of the various forms of urethane or nylon bushings are similar in function, though the durometer can vary even within the realm of polyurethane; generally, the more serious the application, the higher the durometer. Of course, the trade-off is in ride quality. Removing compliance from bushings means that road imperfections are transferred more directly into the chassis. On a race car, this isn't really a concern, but on a daily driver, you might not welcome the harshness, particularly if the car in question isn't regularly used for aggressive maneuvers. Most of the aftermarket urethane bushing kits designed for muscle-era cars are intended for street use, so they still offer some compliance. Polyurethane has been known to create squeaks in some instances, which is why some companies offer graphite-impregnated pieces or some other form of lubricated bushings.
For your front suspension, you will indeed need to swap the steering linkage in your Falcon to that of a V-8-equipped car, and it's fortunate that you have a '65 V-8 donor car, since those parts are actually more common (most are the same as a '65 Mustang), and therefore, more serviceable. If you intend to keep power steering, you'll need to use the centerlink from the Comet, along with its tie-rods, pitman arm, and idler arm.
To convert to Granada-style front discs, you can install the Granada spindles onto your control arms (though now would be a good time to install new ones, which should be spec'd as '65 units). To connect the steering linkage and retain power steering, use a Granada outer tie-rod end on the passenger side and a special conversion outer tie-rod end on the driver side, available from Mustangs Plus in Stockton, California. An alternative would be to convert to manual steering, which would allow you to use Granada outer tie-rod ends on both sides, but you'd have to swap to the manual-steering centerlink. Since the centerlink is the one piece in the '65 front suspension that is unique to the Falcon/Comet (these cars are narrower than a Mustang) they can be difficult to find in decent condition. Fortunately, Falcon Enterprises offers a new reproduction V-8 manual-steering centerlink. Mustangs Plus also offers a trick little hard line-adapter kit that allows you to link the original drum-brake hard lines on the frame to the disc-brake flex hoses rather than having to bend all-new lines. This is necessary because the drum-brake flex hoses connect to the hard lines forward of the spindles, while the Granada disc calipers are positioned at the rear of the spindle. Of course, you'll need to switch from your single master cylinder to the proper dual-reservoir master intended for front discs. Mustangs Plus can also help you with that.
Finally, your Comet power-steering setup can be connected to the late-style power-steering pump from the Fox Mustang, though you will probably need to have a custom hose made for the pressure side.
The Shake That Wouldn't LeaveI recently swapped the 327 in my '67 Camaro for an LS1 with a stock six-speed. I got everything installed without too much trouble, but once I got everything driveable, I found it had a serious vibration problem. Now, with exception of the motor, tranny, and driveshaft, everything else is the same as it was before I started this project.