Do they line up with the braces underneath?

All of the original running boards have those 4 divots or dimples....it was part of the manufacturing process for the attachment points to the support brackets.   I've done quite a few of them and have used Bondo (body filler) to fill them once everything was down to bare metal and thoroughly clean.   Hope that helps.

All the Best, Chip

@tiny Yes, they line up with the supports !

@w-l-chip-boyd - Thanks Chip ! I was wondering about after-market running boards or whatever! Will the 2 part epoxy adhesive stick to the bondo ? There will be bare metal all around the divots/dimples, although they go pretty close to the inside edge of the running board. I don't want to mess these mats up !

I have restored four sets of running boards using that technique and the epoxy adhesive and had no problems.    Others may have another idea, but that one has worked for me.

All the Best, Chip

@w-l-chip-boyd - Thanks Chip ! Any tips for applying the adhesive and the mats ?

When using the polyester fillers like Bondo, I prefer "All Metal" because it has metal filler not clay. It is a bit harder to smooth and sand but does not attract moisture that can cause failure. Epoxy fillers are better but much more expensive and harder to find. I make my own as I have access to the basic materials and having worked to one of the largest epoxy manufacturers have sources that others do not.

Hello RW,

My luck with Bondo is hit and miss. Either I make too much or not enough or get the mix ratios incorrect. Harden up before application is finished or won't harden for days. I know that I can't blame this on anyone except myself. It does cause frustration and expense though. Maybe you might consider an application of an equal 50/50 epoxy mix with a thickening filler for those divots. This is used a lot in marine fiberglass applications as a filler. Just putting that out there so that you might research this alternative.

Polyester body filler is very durable. There are two keys to that durability. Preparation and mix ratio. If both are correct it'll last forever. If either isn't it can fail. The mix ratio is fairly simple. Each can comes with a tube of hardener. That tube of hardener is designed to mix the full can. There is no gauge but if you take a couple of dips of filler and mix in a half tube of hardener it's obvious the ratio is off and the end product will probably fail. Experience is the best teacher as to what works and doesn't. I remember when I was in trade school in the 60s, I was working part time at Feld Chevrolet in Kansas City Kansas in the used car body shop. Work was slow so they sent me to the sales office to use body filler to patch the concrete steps to the office. When we passed through KC on vacation a few years ago I detoured by the old car lot. The dealership is long gone but the sales office still stands. My step patch is still holding strong all these years later.

Chip, Harry, and Tiny - Thank you very much for the tips and info. My nephew is a body man, I'm sure this will make more sense to him, and should save me time and money. 

I removed both running boards today, all the nuts and bolts came out easily, except for one bad actor on each side. I used my Dremel with a cutting wheel and in a few minutes the stubborn bolts were gone. Taking them to be blasted tomorrow, then some paint on the underneath and edges. Next week I hope to be putting on the mats.

Robert the filler will probably be just fine as long as there is no way for moisture to get at it from the back side (no pinholes in the divots)  

What color burgundy is on your car, it's sharp!