You have to find a glass place with some old guys and/or specializes in hot rods. 99% of the windshields most places see are glue in (which is an option on your 70 esp if you have a high end build).
Also, I recommend bringing them a copy of the install instructions from the factory service manual. I don't have one but have seen the page posted on this site before.
I went by my old favorite glass shop the other day to find the guy had retired and sold it. When I told them what I needed the guys said wait a minute, I'll have to get that old guy to help you. There was only one guy left working there who had ever installed a rubber surround window.
It's almost as bad as trying to find someone to tune a carburetor....
Anyway, explain that the windshield has rubber around it and has to be roped in, and you want to make sure they have someone who has done it.