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
 *
 * All widths are using percentages making the grid
 * responsive to most resolutions.
 * 
 * http://lesscss.org/
 * http://960.gs/
 */

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

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

@gutter: 20px;

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

@columns: 12;

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

.container {
    margin-left: auto;
    margin-right: auto;
    max-width: @document_width;
    width: 92%;
}

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

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

.grid(@col: 1, @context: @document_width) {
    width: (@column_width + ((@col - 1) * (@column_width + @gutter))) / @context * 100%;
    display:inline;
    float: left;
    position: relative;
    margin-left: 10px;
    margin-right: 10px;
}

/*********************************************************************
 * 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;
}