Prep work consisted of sanding, sanding, and sanding. I used one of those combo Black & Decket Finishing/Orbital Sanders with the Pointing Oval Sanding pad most of the time. I progressed from really rough stuff 50 grit, majority of work was done with 80 grit progressing to 120 and then hand sanding to 220 prior to painting.
Really tough rust stuff I handled with one of those zip wheels, plastic abbrasive pad that goes on a drill, or if it was really bad, grinding down welding slag either a grinding wheel on a angle grinder or a flap disk on the angle grinder. Filling screw holes for eg. insert screw into hole, cutoff with dremel tool, use welder if appropriate to secure screw in hole, grind down using grinding wheel followed by flapped disk. Usually grinding down created sufficient friction that screw and surrounding metal are merged together.
Anyway, BE Bonnet was surface rusted and underneath I wasn't sure what type of surface was underneath. Remeber this bonnet was sandblasted, primered, and sat for 20 years. Bondo underneath was unsanded in many areas and I had to grind away just to see what was underneath. In many areas I went to bare metal and primed with simple Rustoleum Primer in a spray can, Simple and easy, sanded with 150 and then 220 to smooth out and remove surface "dust" from priming.
On the body, paint was in not all that bad shape. I simply sanded, fixed bad areas, welded in patch panels, ground, and ground, filled and sanded. Just takes time to get the base prepared. Your end results are totally dependent on the quality of the prep work you do underneath. You can't cover crap base with extra paint. You've got to be smooth underneath to get a good finish job.
Expoxy and build up primers. Would have loved to have used them and sprayed them. Would have had a much better job. Unfortunately, wife's asathma and intolerance for stinky, smelly stuff plus the need to protect oneself in using these great products precluded their use. I've got a one car attached garage under the house. Smells go straight up and I could not risk compromising my better half's health. Another is cost, epoxy and buildup primers are not inexpensive. Byproducts are hazardous to the person behind the sprayer.
As I mentioned at the beginning of this subject. I made a decision that no matter what I do and how much prep work I put into Bugsy, he will continue to rust. My job is to slow down the decay and self destruction process. I do not have an unlimited budget and I'd rather be driving than painting and sanding.
Others on this forum ascribe to a different philosophy and want their car concours. Each end of the scale has merits and this hobby has room for all. I'd love to have Bugsy be restored to Miss Agatha's condition or be able to restore like Frank C. is able to knock out in short order. I don't have the facilities, environmental conditions, time, or budget to do it all. Spridgets even in concours quality seldom exceed $5,000 maximum price. Bugeye's are the exception. I did the cost vs. value equations and a $2,000 paint job did not work.
I love being able to tinker in the garage with Bugsy but more importantly I'd rather get out and drive him. Rustoleum Technique works well for what you get out of it. Bugsy came home with 5 different colors of paint on the body and was ugly. I drove him for 6 years in multiple shades of paint as I could not afford multiple thousands of $ for someone to spray him properly. I discovered the Rustoleum Blog and tried it. It worked for me and I was finally able to get Bugsy all into one color. He is a 10 footer and that is all he will ever be but I do love driving him. Bugsy is 40 years old and the bonnet is 50 years old. These aren't new parts and my skill level is not that great but I am all in the same color with only a few rusted areas still to be fixed next winter. Again, get it done and get out and drive. Enjoy this LBC Addiction, we all get different things from it. More importantly we have fun. Get out and drive!!! Off of my soapbox.