Ended up getting one from these guys.
http://www.gmitopdesign.com/
I'm sure there are a few differences in a '75 hull and an '89.
I ended up with a 6' top, that would work on a 79-84" width and had a height of 48-54". Ended up cutting off 6" to make me happy with head room and fitting to the area I wanted.
I made it to fold forward or rear with hard adjustable pole supports and it not fastened to the windshield.