Lots of options
Depending on the condition of the underbody, you have a few options in cleaning and prepping the underside. Not sure how much corrosion you have, etc. but to start the process I generally put the car on a lift and do an initial inspection. This will tell you the condition of the underside and what areas might have deteriorated more than others.
First I generally powerwash everything with a high pressure system. I f you have lots of oil, you might want to prep those areas first, some like the aerosol cans of degreaser. some add a degreaser passed through the high pressure gun. After this you should have a better picture what might lie ahead. If there's undercoating, and you want to remove it, plan on spending a lot of time heating the stuff and scraping it off and getting rid of it. If it's just oil and grease, you are lucky!
Corrosion is of course the worst. You have to decide whether to cut it out and replace, or prepare and seal it somehow to deal with it another time. Eventually someone will have to cut out the corroded sections and replace them as needed....
After you've thoroughly cleaned everything, you need to think about how/whether you might want to coat those newly cleaned surfaces with either something to protect it or something to make it look original, or something to look pretty, whatever. That's your choice. Lots of parts and colors and shades of black to consider here. Do you remove the shocks and springs before painting the underside, that sort of thing. How do you treat the wheels and brake drums? Are you aiming at a faithful restoration, or trying to save what is left, or some thing in between? Some guys go for the "Dupont overhaul" which is the quickie cosmetic coverage of parts with rattle cans and little preparation. Nothing wrong with that (unless you are hiding something and trying to sell it). What is it you are going for?
You have lots of choices, lots of degrees to consider, lots of paths to get there. In the end you'll be glad you cleaned and preserved another X frame car. And then you'll swear you'll never do it again, until the next one comes along
.
Good luck!
TomK
: Don't we all wish we had a body tilter? When I did my 64, I sand blasted some of the crud off, also used many drill powered wire brushes. Any place there was under coating I used a propane torch, and a scrapper. It was one of the worst things I ever had to do. But like they say, somebody has to do it.
Laying on the ground with debris falling on me, and in my clothes had me talking to myself and the car. Just remember to protect your eyes, and lungs at all times. And try not to start a fire.
When your finally finished, you'll be amazed.
Good luck Skip
:evil 
