Brad, your not leaving us are you??? lol
I've got a stock 87 GN, and I don't see any reason why the intercooler wouldn't bolt right in to a hot air. You probably wouldn't want to get a stock one with all the better flowing aftermarket ones available, but I'm not the right one to be commenting on that. It looks to me like it would be a matter of picking up a couple of the mounting pieces from a 86/87 for it that bolt onto the bottom, (may have to reclock that oil cooler adapter you just got), pick up the air scoop that bolts onto the bottom, cut a slot in the bottom deflector and modify or buy 86/87 front air dams. Get the special crank pulley that has the fan on it. (will just have to use the center piece remember being they have the one serpintine belt.) Accesory wise, Doesn't look like you should have any problems with clearances, except maybe for the inlet side might have to be cut down or modified. From what I have noticed here and there in post, those goose necks on the stock intercoolers are restrictive anyway and are normally the first thing to get modified. but don't quote me on that.
Any pictures of my 87 you need, just let me know, and I'll try and help best I can.
btw, why not just a front mount intercooler? You could buy one with a kit that comes with everything to mount it. You've already done the ramchargers and fbod conversion, cooling shouldn't be a issue. Then you wouldn't have to worry about it getting heat soaked, and theres a couple other benefits, but theres plenty of info on that on this board.
I've seen LimitedLTD's front mount set up, and it just looks wicked with those 2 big pipes going down in front of the engine down around in front of the radiator. (which helps fill up that big gap in front of the engine too.