LessCSS and 960gs don't play well together normally. Here's the definitions for 960gs to let LessCSS work with it. Looks like we can pull all grid data out of the HTML.

960gs.less

/**
 * A LessCSS version of the 960 Grid System
 * 
 * http://lesscss.org/
 * http://960.gs/
 */

/*********************************************************************
 * Settings                                                          *
 *********************************************************************/

/* Maximum width of the document
 ********************************/
@document_width: 960px;

/* The gutter width
 ********************************/

@gutter: 20px;

/* Number of columns
 ********************************/

@columns: 12;

/*********************************************************************
 * Container                                                         *
 *********************************************************************/

.container {
    width: @document_width;
    margin-left:auto;
    margin-right:auto;
}

/*********************************************************************
 * Grid                                                              *
 *********************************************************************/

@column_width: (@document_width - @gutter * @columns) / @columns;

.grid(@col:1) {
    width: (@column_width + ((@col - 1) * (@column_width + @gutter)));
    display:inline;
    float: left;
    position: relative;
    margin-left: @columns / 2;
    margin-right: @columns / 2;
}

/*********************************************************************
 * Grid >> Children (Alpha ~ First, Omega ~ Last)                    *
 *********************************************************************/

.alpha {
	margin-left: 0;
}

.omega {
	margin-right: 0;
}

/*********************************************************************
 * Extra Space >> 2 Columns                                          *
 *********************************************************************/

.prefix(@col:1) {
    padding-left: (@col) * (@column_width + @gutter);
}

.suffix(@col:1) {
    padding-right: (@col) * (@column_width + @gutter);
}

/*********************************************************************
 * Push & Pull >> 2 Columns                                          *
 *********************************************************************/

.push(@col:1) {
    left: (@col) * (@column_width + @gutter);
}

.pull(@col:1) {
    right: (@col) * (@column_width + @gutter);
}


/*********************************************************************
 * Clear Floated Elements                                            *
 *********************************************************************/

.clear {
	clear: both;
	display: block;
	overflow: hidden;
	visibility: hidden;
	width: 0;
	height: 0;
}


.clearfix:after {
	clear: both;
	content: ' ';
	display: block;
	font-size: 0;
	line-height: 0;
	visibility: hidden;
	width: 0;
	height: 0;
}

.clearfix {
	display: inline-block;
}

* html .clearfix {
	height: 1%;
}

.clearfix {
	display: block;
}