That was my concern too. If there were a larger flange to bolt a block of steel to, then it might be easy to extend. Skipping the quick hitch is looking attractive at this point.I've been to four or five tractor dealers in this area. Longest pins I've seen were probably 6".
OR - have special pins made at a local machine shop. However - having the attachment points for the quick hitch spread that wide could make the entire "hook up" rather fragile.
5030 - has the best suggestion.