Be very carfull and work with 2 people, make sure the molding or seal has been cleaned and make sure you pull the support lip out in the front face of the seal with a piece of wire or better yet a pick tool something small once that lip has been opened up it should give you more flexability to work the seal around. set the lower seal on the steel first and get the window sitting in the groove a third person could help you support the inside so the window does not slip inward. Use pick tools or small screw drivers Carefully to work the seal around the sides far enough to hold the glass. when you get it worked all the way around start to push that lip you released earlier and reinsert it under the existing lip this is what provides support and strength to keep the glass in place glass cleaner can help lubricate the rubber to more easily slip your pick tools don't appliy to much pressure and you should be ok
Use a new seal...the old ones can be a real handicap because they are usually stiff.
Best thing to work the seal around is a plastic 'window tool' that's made for window glass installs..however I've used small screwdrivers before..you just have to be careful not to chip the edges or bust the glass!
Use new seal if possible, use lubricant and use rope. Tin rope, feed into the seal groove, and start installing the windshield from the inside of the cab, start with the lower part, lover right corner is where you want the rope ends to stick out. start puling them so that the seal is overlapping the windshield frame. you can try to work both ends simultaneously, sporadically, ....get the feel for it. gotta have the helper inside the cab.
BTW, I've never done it on SG2 cab, but did many windows of that design on cars and other machines. Good luck