Not sure what your old windshield gaskets look like but if they are original than would be a good Idea to replace them.
I have installed a lot of glass and it is no fun when you use a new gasket and I am not the best at it but if I were you I would find some one in your area that knows what they are doing and pay to have it done right I think you would be money ahead in the long run.
If you break the glass you will pay for it but if they break it than they pay for it, but make sure they will.
