I bought two 320 windshields from Wayne's group buy, cut by a fella in LA. Wayne had 18 windshield made up by this fella named Kotta(sp?) and I think they were cut down from a Plymouth minivan windshield. Awesome quality.
When I needed a 521 windshield, I ordered three from Pilkington classics, back east, and they were shipped together to Santa Clara from England.
I bought one and a spare for my 521 project, and I sold the third to Ray (Mrbigtanker).
I am told some of the windshields available stateside are slightly thinner. I wanted the Pilkington version as it was known to be very high quality and the exact same thickness as stock. The Class division fella told me they bring them in about 50 at a time. Call their toll free and ask for one of the two glass guys. They both seem to be very long-term Pilkington employees and were really nice to talk with.
I still have that spare for piece of mind. Just this evening my wife moved the spare couch to vacuum in the study, and asked me why we have a windshield trussed up in blankets stashed behind the couch in the study:)
BTW: Three windshields came in a very sturdy crate. I should have kept it, it was built like furniture.