Formatting for atypical letterhead

[Jason]

Hi:

My company's letter head runs along the top and 1/3 of the right side (so
the top right corner is sort of the anchor point with our logo and lines
going horizontal and vertically.)

I want to create a template. The top part is easy, with a margin to
incorporate the header of about 1 1/4", but how do I format the right side,
so for the first 1/3 of the page, the right margin is in about 1 3/4" and
then to have the rest of the page with regular margins?

Thanks for your help!

Jason