Suburban Side Windows

[Big Fenders]

Ive got a 1960 GMC Suburban that I want to replace side window glass...most was broken or missing. I plan on having two fixed [one on each side] and two sliding. It seems the the best rubber is from Steele and I know a little pricy but Iv'e fought with cheaper window seals and learned the extra money is worth it. I did remove the window tacks [frames] and cut out rusted through areas and replaced. Question is...do you install the windows in the frames with new seals and then bolt the assembly in the window opening or do you bolt the frame in the opening and then install the glass and seals?
Bob