Running Board Help

The mounting flanges on the bottom of my running boards are rusted away. Can someone let me know how far apart
the holes are and the distance to the one hole to the back bumper flange (6.5" mark on tape measure). I am trying to save myself the hassle of mounting everything back on the truck to see where the holes should be. I want to weld nuts to the new flanges before welding them to the running board. Since the Running board mounting braces are slotted...I have some play to work with.

I had to attach pics in multiple posts. Picc too large.

Running board brace

rusted flange

It might be a god idea to mount the struts on the frame and place the running boards into the place where they will be then mark the locations, as required. If the raised section on the underside of the running boards are rusted badly, remove them completely and carefully grind the surfaces smooth. I like the WALTER FLAP WHEELS. Now you can buy some .125" wall square tubing. about 1 1/2" square and split it to form the missing parts. do not be worried about the replacement pieces now looking like toe original , that is not important. The new part can be carefully welded in place after the running boards are mocked up, in place. (refer to the first sentence) If you are uncomfortable about welding up-side-down, mark the locations of the new pieces and remove for welding. This is easy. Been there done that.
A company called AU-VE-CO has thousands of blind fasteners that might make you job easier. Use a little NERER-SEIZ on all of the fasteners. A little goes a very long way. A $7/ 250ml jar could last you for a decade or more. the sun is out and soon I will be out also.

Thanks Nik

I like the tubing idea. I will order some. I had planned on grinding off the rusted mounts and having the running boards media blasted.
I messed around with some stick welding when I was a kid on my grandfathers farm
but never welded enough to get really good at it. It was good enough for patching some farm equipment but the welds were ugly.
I am considering on getting a small Mig welder and taking a course at the local vo-tech. Could prob get all the tips I need off of U-tube.
There again....take practice and time to get good at it. Thanks also for the blind fastener tip.

Check Craigslist in your area for some good deals on welders. When I bought my first welder a good friend insisted that I buy MADE IN USA because it is important. I have had my MILLER-MATIC 200 for over 30 years and it still works really well. A good wire-feed (mig) will make your welding look more professional. Welding tips and tricks.com with Jamie is on You Tube and like you suggested, some local adult education. The new MILLER welder have gone electronic and while I hang onto my old 200, I have to say these new welders really work well because there are more adjustments for start and stop "ramping". I do not like flux core in a home machine because it has become an entry level POS in many cases. There is flux-core in heavy industry, but that is not us. Some time abo, I bought a MILLER 180 SD and I have never regretted it for a second. TIG welding was the nest natural move up and TIG has taken it to the next level, for me. The 180 SD will stick weld and do AC and DC TIG. The later model 200SD is even better. Don't reject one of those small suit-case size MILLERS. They are worth their weight in pure magic.
MEMCO and USA MADE LINCOLN are also really good. I have this thing about not buying anything from off-shore unless there is absolutely not option.
It might be a good idea to burn a few holes in some practice scrap, first.

As usual...a lot of great advice Nik. Thanks a bunch.