Glad to see you haven't been put off from your horn-loaded endeavour .
Here's a nice thread ( over at DIY ) for a bit of inspiration . ( Click the pic )
It's well worth the read time to understand the story behind this particular pair of BLH (back-loaded-horn ) Jensen copies.
One of the beauties of the pictured system is that because the front baffle ( holding the woofer & horn ) must be removable it allows a person to try different horns in place ( to find what works best for their situation ) .
I happen to like Radials ( particularly the throat-less variety / first championed by W.E. post WWII) .
I listen to an Altec 288-8K through an Emilar EH-500-2 Radial Horn ( using a 1.4"-2" adapter ) .
BTW, Brazilian clones of the QSC horn ( seen in the first pic ) are being blown out by P.E. for a measly $10.00 USD .
Canadians will want to purchase them through P.E.'s eBay store front ( it's the cheapest shipping into Canada since it goes through the Global Shipping System ) . ( Click the pic for the link )
Forget the original ad-copy for this horn, it's a planar ( mostly conical ) wave-guide ( with no exponential curves ).
- The biggest knock against it ( being planar/conical ) is though it's big, it barely affords a 1K crossover point ( not really a problem when using 130's / 2220's ).
Here's an expensive ( almost throat-less / QUICK-ENTRY ) Radial close in size to the 811b that you mentioned ( & a lot more affordable ).
I consider this a great project-horn opportunity.
Click the pic! ( again this seller uses the Global Shipping System available to US sellers that saves You & I money/ plus allows one to figure out actual "Landed Costs" since this includes taxes, duties & brokerage ).