Hi Nick and welcome to the vintage Airstream hobby. I believe you picked the right website to learn all about your 64 Ambassador 28'. I've used VTS a lot with good success for parts for my vintage trailer. I believe the 64 model year had flat glass windows which will be easier to replace the glass.
You might enjoy reading all about your Ambassador in the Airstream Trailer Forums found in the Knowledge Base found near the bottom of the Forums tab. It is an area where the conversations are all about repairing and renovating various models and model years. Here is a link to the 64 Ambassador section.
https://www.airforums.com/forums/f118/
I make special note of steinVT and his 62 Ambassador. He is from your home state, and he is very good at renovating vintage Airstreams.
Here is a photo of my 75 Overlander 27' on its maiden voyage after my renovation two winters ago. These old Airstreams get under your skin.
David
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WBCCI #8607 VAC Region 11
KnowledgeBase trailer renovation threads: 69 Globetrotter, 76 Sovereign, 75 Overlander, 66 Trade Wind Such fun !