Good Morning Chris,
first on the washers you want to use, you would be better off using either internal or external star washers. (they have teeth that dig in to the bolt head and whatever they go against )
Here is a picture of washers
You don't want to use a regular split one, the other two would be better for your application along with the loctite.
Belville washers won't work for your application, they are used more for a cushion and don't have enough holding power for bumps.
If you use what I said you won't need the welding and your right Vandenberg doesn't do welding but do have replacement parts if needed.
That is the reason I don't want you to weld it,what happens if it broke?
Well you wouldn't be able to replace part and have to purchase a new one because of cost to grind weld off and re-weld.
Here is a link for place that will weld anything that can be welded in your area.
Just click on the square box for a business card that's shows address and phone numbers, I used your zip so should be close to you.
I think you should try other suggestions first if it still will not hold you can always get welded at another time.
Anyway it was very nice of you for the kind words you said about me and I wish you good luck with your project.
If you ever need something you know where to find me.
God Bless spanky