You could just use a margin-left with a percentage.
HTML
<div class="goleft">Left Div</div>
<div class="goright">Right Div</div>
CSS
.goright{
margin-left:20%;
}
.goleft{
margin-right:20%;
}
(goleft would be the same as default, but can reverse if needed)
text-align doesn't always work as intended for layout options, it's mainly just for text. (But is often used for form elements too).
The end result of doing this will have a similar effect to a div with float:right; and width:80% set. Except, it won't clump together like a float will. (Saving the default display properties for the elements that come after).