Fraziers were made here in Dallas,Tx and his designs were good. For the most part he used Utah drivers and though I really liked the little 2 ways hey made with an 8" woofer and a 3" tweeter (8 ohm drivers with a 3uF high pass on the tweets, so you figure it out) that he sold in black boxes that you finished yourself. They were an early 60s design because I bought a pair from a guy who bought his in 1962 in Norman Okla, so maybe a late 50s design. They played and sounded great, but were the best Fraziers I ever owned, including Dixies.
I think there is an 8" driver in the middle of that horn, the compression driver on top is cheap, the horn made from plywood if they are like the ones I have seen and since the VCs are not on the same vertical the phasing is a bit off.
All in all it is a good design for a horn in a small box but there is I think 2 folds and the length of the horn isn't long enough for low frequencies (like below 30, but I would bet not below 40) so putting a long excursion 8" sub driver in there might not get you lower frequencies, then again when it was designed only audiophiles that listened to organ music really cared about extended lows.
A great design that could easily be improved on, there still isn't a great following on Fraziers but he did design and make a few large high end speakers as well as pro sound like you have there.
I found some in Little Rock and bought those and some Altec horns and compression drivers which paid for the gas for the road trip. There was a Harley Convention in Hot Springs and it will be coming up quick. Get some ear plugs and go. It is loads of fun, but the upper end where the springs are is a canyon about 1/2 mile wide at best and when there are 10,000 Harleys in there with no mufflers it gets really loud and stays loud after they turn them off because of the echos. Nature's reverb.
Thatch