I've used Sled City (Larry's) race weight glass parts on 3 race car projects ('64 NSS Sport Fury and 2 NSS Cudas) over the past 6 years and I haven't had an issue with quality or delivery. I call Larry and he gets me what I need in the timeframe I need it. And this testiment comes from someone who is extremely fussy.
I've used Glasstek and AAR (for bolt on glass panels) too, both good companies. I would reccomend them as well for "bolt on panels".