would it just be better to use urethane?
It is my understanding that urethane degrades in direct sunlight, hence the blacked out edges on all window glass today. I could be wrong but that is what I heard.
If that's true then the Butyl tape is better for our old cars.
If not then urethane would work fine but I don't have the finesse to use the application gun very well. For you it may not be a problem.
If you do the butyl tape and it doesn't go in correct do not try to reposition it. Cut it out and redo it. I had a friend help me and busted a windshield. It went in a little off and before I could say don't he tried to press it back out and snap.