68 SS Door glass or lexan ? your idea ?

IMO, if you're trying to get as perfect as possible (and assuming the financial responsibilities that come along with that commitment) - then order the custom real glass. If you're building a tribute car that you plan to drive and race and money is a concern - then go with Lexan. Lexan will not last forever but if you're careful you'll get a lot of good years from it - good return on investment. Ultimately - it's not "right" if you're after factory as-delivered but most won't make that investment on something you will never get back if you sell or might break if you race.