[Antennas] 160 vertical capacitance question

[W0DXZ at aol.com]

I have a metal pole, insulated from ground  (a vertical  antenna) about 50 
feet high, with  4 ,4 foot long capacitance hat rods on  it  (get that?) How to 
feed it, etc?
 I plan on feeding it with either,,, coax, or "open wire  line", 300 ohm.
Now, the question is, I think I have to add some capaitance at  the base of 
the vertical... how much?  I was thinking of adding  a 350mf  variable,,, is 
that the right ball park? Then running the  coax or whatever into a tuner in the 
shack. Hoping the 350mf  will get it  close,.,, any help?
I have this great vertical, just dont know how to feed  it,,,
73 Bob W0DXZ