I agree with many ideas above, Always use rubber spacer blocks and butyl rope on gasketless glass. Do not use a tube sealer to install them.

Let's talk sealant, It is most important. The car will flex, the gasket will surely flex, so I believe a hard curing sealer is wrong for a gasket installation. that pictured urethane is for Late model vehicles, not for this application, ask a competent glass shop guy who spent his career in this industry. Bedding and glazing compound seems to always leak in my experience.

I used a liquid butyl which stays flexible. My oldest install I still own stayed leak free for 14 years in a daily driver parked in the weather B-body, just started leaking at drivers corner.