Hi Jeff,
            given your experience with 1 inch tube and 4 port dividers , a 
quick look at this suggests the following....

1/4 wL lines...so use 1/2wL centre fed......at each end place 3 connectors 
soldered to the inner tube just as you would place 2 for a 4 port divider. 
The centre conductor now needs to present  40.8 ohm......I don't have the 
formula handy but I'm sure you do...If not let me know.....hopefully you can 
find suitable diameter brass or copper....

In the past I have had to use  32mm square  of varying wall thickness to be 
able to accommodate the copper tubing I use for the inner to arrive at my 
line impedance.

Now the only problem with this approach is there are 3 connectors on each 
side and there is no symmetry in feeding the antennas......
One way around this is to "cross feed"  the middle yagi  .  This helps to 
make sense in getting equal 50 ohm line lengths to each antenna from the 
divider.  It's also better to use a 3/4 wL long divider on 432...that way 
you have less line (less loss)  to each antenna and  it will be identical to 
the 144MHz divider.  Make 2 at the same time!

I hope this helps......If you need more help with finding the formulas for Z 
of round tube in square guide, then let me know....I can dig it out!

Regards
Charlie
VK3NX