Sweet Baby Jesus. This hits a VERY sore spot with me. When I tried to install my windshield in my '55.1, it also would not fit. Seemed too big for the gasket. Had a pro try it...three times, then another pro...no luck. Then a third pro in a small shop behind his house. Real low-life kind of guy. Had my truck outside for over a week with the windshield out in the elements (assh**e). He announced after several attempts that the glass was too big and needed to be "shaved" 1/8" all the way around on his big standing belt sander, but he was out of belts and was waiting for a delivery. Finally gets it in (deluxe cab with the stainless trim in the gasket) and tells me he didn't put any urethane in the gasket because he wasn't sure if it was going to go in or not. So the glass finally "pops" into place and it has no sealant. Leaks like a freaking sieve but at least it's in. Since my truck is in the "beater/work truck" category I run a bead of silicone around the windshield where it meets the glass and one around the gasket where it meets the body. There was simply NO way I was going to be able to fit the tip of a urethane tube between the gasket and the glass and the gasket and the body.
Finding a GOOD auto glass guy around here that knows how to work on classic stuff is nearly impossible. I know a lot of people in the hobby around here and they all say the same thing.
Good luck finding that person. It is very likely that the glass you have is indeed too big.
Andy