After speaking to Ken Scott this morning I feel much better. He advised me to go ahead and rivet up the horn brace with the 470s again despite the dimpling/countersinking I had "custom" done. He reminded me that the 470s would still be much stronger than the pop rivets which are an alternative for the hard to reach places in the horn brace.
The riveting went well and I was pleased with the result. It seems that my previous thoughts of "just chucking the whole darn thing and starting over" were a bit overly dramatic and premature.
In the future I will definitely be much more patient and suspend work ---and call Vans before I create a problem. The detailed notes help as well as you never know if what you thought will be just a few days until building again turns into a few weeks