I need to install a new cowl vent gasket on my'34 before the windshield goes in so I have easy access. I dry fitted it earlier and it was bit of a pain to position. My question is: what adhesive should I use to hold it in place?

Try the black 3M weatherstrip adhesive.

Well, the gasket went a bit easier with the addition of my wife's two hands. But when one thing is easy you can expect the next step to be a pain. I had a glass guy come out to help me install the front and back glass. The back went in easy but the front glass was made a bit too large. When my father-in-law got the car back in 1979, the windshield was missing so the guy who made him a new one evidently was guessing a bit. At least it was too large. It can be "sanded" down to size. But I will have to pay for that and a second visit with from the glass guy. I also learned the garnish moldings hold the glass in place so I am wondering how to hold it in place, without the molding, while it is being upholstered?

If the windscreen garnish needs to be removed to do the upholstery I would leave the glass out until the upholstery is done. You could do a trial fit of the glass but would mean a third visit by the glazier though.
Tony

The glass guy suggested making some small wooden blocks and screw about four of them in place to hold the glass while the garnish moldings are out. Has anyone done something like this or have a better idea?