Welcome to the forum - and congratulations on your rig. You're starting out right!

I am listening to the 803B horns right now at about 3m distance and they are fine. The 803 is a very directional horn, very tight - so it does not splash off the wall much. The 1505 that Hiraga uses is much wider - and I think a bit flatter at the top end. The 803B will play lower, but drops off at the top end. so the crossover for the 1505 is not ideal for the 803, although it is a good place to start.

Anyhow, the 803 is a great start and is often much cheaper than the 1005 or the 1505.

just FYI - I'm the guy who helped Mr. Hiraga rebuild those A5s. See my avatar. Of course that was a few years before you were born! =)