You deal with it with hope...
Setup your printer for the custom size 10 x 7.
Create your card as though it was a landscaped 10 x 7 publication. From the
Arrange menu, set your margins Click the grid guides tab, 2 columns, spacing
twice the margin (if your right margin is .5, set the spacing to 1 inch, check
add a center line between the columns.
Create the front of the card with the design on the right. Put the colophon on
the left.
On the inside, the standard message will be on the right.
Do not look at print preview until you are ready to print or you will be upset.
From file, click print, be certain all your settings are correct, NOW look at
print preview on this screen, it should preview correctly. You can cancel out if
you need to make adjustments to your card.
Print the current page, turn the card over, go to page two, print the current
page again.