The underside of my car was painted semi gloss black from the bottom of the
firewall to the rear trunk pan.  When the body was painted, overspray got on the
bottom of the car. There is red paint that fades from the rockers toward the
driveshaft hump.
Plan A was to get a rotisserie from a co-worker, but he had already sold it.  Plan B
was to have the body man do it, but that was going to be an extra grand on top of the
paint total.  So I decided to do it myself and save a few bucks.  I did all of this laying
on my back using a DA and some wire wheels to take off the dirt and rust from the
floor pans.  If I was a big time resto guy I could have got a rotisserie and a power
washer and been done with it.  The car is mint underneath.  I started with the firewall
and moved my way back.  You really havent got dirty until you have attacked 40 year
old dirt with a wire wheel on a die grinder.  Trust me.
I used PPG DP90LF to prime the floor pans and firewall.
Firewall painted with PPG DDL 9423
Next step was to apply red paint to the areas that got oversprayed when the car
was painted at the factory.  The factory process was to get color on the body no
matter where else it went.  I found red all over the bottom and inside the wheel
wells.  I put it back in the places I found it.  I then top coated everything with flat
clear.
I used 3M Body Schutz to recreate the undercoat used in the wheel wells and on the
trunk pan behind the rear tires.