[TowerTalk] 40 meter rotating dipole question

[Mark, K5ER]

Hi Guys, I have checked the archives, but not found specific answers, so 
forgive me if this has already been covered and I am asking the wrong 
questions. To help a friend, I am building a 40 meter rotatable dipole, to 
live at 90' on his mast. It will be about 12' above his 36' boom 20M OWA. I 
will fabricate a heavy duty mount/center insulator, and incorporate 2 truss 
cables, either dacron or kevlar.
He delivered to me two (used) elements from a previous unidentified 
antenna. Each element is abt 28' long, with the taper schedule going from 1 
1/4 down to 5/8. I have spare material in stock, so I could easily add a 
1/2" x 5' tip to each and end up with a full size dipole.

Question one - The price of material isn't much more, so why does it seem 
that "nobody" builds rotatable dipoles to the full 66-67 feet?

Question two - IF a shortened antenna is better, is there a "better" 
length? I see many in the range from 38 to 55 feet.

Question three - If shortened, I know the ant will be capacitive, and 
therefore can be matched by adding an inductor across the feed.  I find 
many pages of formula with lots of Latin characters, but missed that day in 
math class. If someone had a hint of a starting point, ie> 4" long, 5 turns 
on 2" diam. , or 4 turns on 3" diam, etc. I could then work backwards and 
make this work for him.

I have EZnec 5+, but have only used it to build OWA antenna so far, which 
makes a beautiful direct feed, so I have no experience with adding a load. 
I plan to input the taper schedule into EZnec, but if a given length is 
known to be superior, I am not too proud to ask for it, rather than spend 
hours building model after model working my way through the possibilities.

I understand that height can affect performance and feed point impedance, 
however, neither the owner nor I climb. I need to model and build this 
antenna, and then expect it to work as modeled when the climber puts it in 
place, so any ideas would be appreciated.

Thanks,
Mark, K5ER