Just did mine.(1990 740) The hardest part is getting a good one out of the junker. I paid a guy $20 to get it out and it was worth it. Installation is pretty easy. Just get the old glass and adhesive off. Use a razor knife to scrape and cut the old adhesive almost down to the metal. Clean the area well with thinner. Buy a 3m installation kit from a glass shop, which consists of a role of black adhesive. I used the 5/16" stuff. Stick it to the metal around the opening. Then pull off the protective paper and carefully place the glass. You will only get 1 chance. Make sure the glass is perfectly clean where it contacts the adhesive. Don't touch the adhesive wit your fingers. Replace the mouldings and you are done.
U pull it yards will charge 10-20 bucks but you have to get it out without breaking. Full service yards will want 50 to 125 but they will have it out. The books say you can only use glass from 87-91. I used a glas from an 86 and it fit fine. Defroster grids are different but work fine. I believe all 740s have the same measurements. Good luck.
(Or you can have one installed for $350-$500 by a glass shop).