altec model 19 , how to upgrade the speaker ?

I have a couple of model 19 speakers custom built .
They have 416 8b lows and 511b horn with 808 hf driver .
no crossover .

what should I do ?

my crossover options ,

1.have a friend build a crossover based on specs on the internet.

2. try and find them on ebay .

3. buy iconic 600 dollar xo .

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do I change the 511b to the 811 horn ?

do I change it to any other horn ?

what driver should I use on the horn ?