Do you actually want a windshield, or do you just need it for street legality?
I've been trying to think of something for my chevy for a while. I've thought about maybe doing a flat plexi shield, and just have it "roughly" where the original windshield was. As far as I know, there's no way to secure a glass windshield to your cab that's not semi-permanent.... I'm no expert though
I have a couple hot rod buddies who are trying to get me to just put a 6" windshield on it so it's legal. Evidently that's all you have to have to be legal in CA
It is pretty common in some stock car racing circle track stuff. Instead of the glue or older weatherstrip style you have to find a flat soft material to make a bed for the windsheild to sit in so it doesnt hit any sharp edges etc. They make clips every 6 inches or so that press down on the windshield around the perimeter. Typically they just sheet metal screw them to the window frame. Most race tracks require you also make two straps that go all the way vertically top to bottom of the winshield frame. You prebend these straps opposite the curve of the windshield a little so when installed they lay flat on the window. Works pretty good and easily removed. Doesnt look stock of course.
Depending on your set-up, it shouldn't be that difficult. Either make a steel or aluminum "frame/panel" that will cover the maximum area needed and Dzus fasten or bolt to the car. Cut a cardboard template of the desired shape of the windshield and have a piece of laminated glass cut to the shape of the cardboard. Most reputable glass shops can do that. Install the glass into the panel and use a Trim-Lok gasket:
MAKE SURE TO USE THE LOCKING SECTION... the glass WILL NOT withstand the force of oncoming air pressure. Even if you think you do not need it... USE it. The last windshield I saw come into a car was about 70mph outside Gonzaga going to CoCo's..... wasn't pretty.
On your 75 Chevy, just get a new windshield gasket and lock bead ($40 from LMC Truck) and keep them lubed and they will not stick to the windhield frame, especially if your have it in and out from time to time. Get a lock bead installation and removal tool from HF or an auto parts store for a few bucks. If you are not sure how to remove and install get an auto glass shop to show you the tricks - it is easy.
I just picked up a ranger with an easily removable stock front window... I'll post the pics I have, but I'm at work and away from the shop for a few weeks so I can't get you a really good photo of it.
Basically it has an aluminum post inside the cab dead center for support. An aluminum tab outside the cab and centered to hold the bottom of the winshield in.
There are two rods that are attached to the top of the cab above the pillars and hinged to swing down over the winshield. The rods have foam cushions on them where they touch the glass. Once the rods are hinged down over the window they slide over two 3/8 studs and are tightened down with lock nuts. These rods are to the extreme outboard edges of the edges of the windshield
A foam gasket around the sheet metal keeps it sealed...