Crossover build

Hello everybody, I am a musician in an orchestra without the nessesary understanding of crossover build!
I love to build fullrange enclosures but now I capitulate with my next project.
A friend of mine sold me his Altec 806A/Isophon Orchester combi. Sounds very good!
http://my.funpic.de/show-photo/730429-PIC.jpg
Now I am interested in a pair of Altec 3156 for a original cabinet made for this driver. The 8156X...
Here I already have made from some other cabinets from a AN12 project.
http://my.funpic.de/show-photo/730430-PIC.jpg
I am interested in the sound from these two Altec drivers playing together!

Now my question: When I combine these two, what crossover do I put in front of the 3156? And : can I just remove the 806A driver crossover and put it in the box of the 3156 next to the 3156 crossover tangeled like in my combo Altec/Isophon?
I have the specs of each driver! If somebody needs details...
Greets from germany, chris
 
If your crossover is the N-800D, you should have no problem just connecting up the 3156 to see how it sounds, it may not be the ideal crossover (just a textbook 2nd order by the look of it), but you should be able to adjust the level of the 806 to match.

N-800 schematic:
http://alteclansingunofficial.nlenet.net/publications/techletters/TL_121.pdf
3156 Datasheet:
http://www.greatplainsaudio.com/vintage_altec/3156_lfldspkr_spec_sheet.pdf

re:Is it desired to put a 24dB/octave in front of the 806a just to make sure that 500Hz is lowist to go? " - yes, definitely