I see they have several different lengths on their web site. You said you have the 36" is that measurement from the pivot pin to the end of the thumb? My bucket measurement from top to cutting edge is 24". Probably go with that if it reaches from top to cutting edge when closed. Obviously it won't touch if you have a lot of material in the bucket.
On your angle iron you installed did you drill and tap the holes for the mounting bolts? Or did you weld nuts on the bottom side?
Company is in Centralia, Il. which is a few ours south of me. Did not know that.