When I get back from vacation, I'll look in my stash - I may have a single L1 you can have for cheap (my dad used to use one for a center when he had L7's).
I don't think rotating the horn is going to get you anything unless you also make the speakers a three way and add a tweeter that does not reflect off the baffle, as the Paragon had. I will leave it to those who own Paragons to argue whether the curved baffle/midrange reflection trick requires the old "Ping Pong Stereo" recordings from the old days or if it still is valid with modern recordings.
I'm glad you could set your dad up with something good - My father got the same S7 load when he was in college and built several enclosures for them over the years. When the Lansalloy surrounds dried up, he stopped listening to them, so I got him L7's, then 250Ti's and took his old drivers, which have been reconed and put in L200 Enclosures. They are now doing shop audio duty for me, as he made me promise never to get rid of them. I guess that means they get buried with me