X-Cart forums - How to add extra fields to invoices

We have an extra field "Location" set up for all of our products. This lets us know where in the warehouse the item is located. I know which template to edit, and where to put the code, but I don't know the syntax. What do I add to mail/html/order_data.tpl to have a specific extra field show up? Here is what I've tried:

{$extra_fields[field].field_value}
{$extra_fields[Location].field_value}
{$extra_fields[$product.Location].field_value}

Code:

{foreach from=$products item=product}

<TR>

<TD align="center">{$product.productcode}</TD>



<TD align="center">

??????

</TD>



<TD><FONT style="FONT-SIZE: 11px">{$product.product}</FONT>

{if $product.product_options ne ''}

<TABLE>



<TR>

<TD valign="top">{$lng.lbl_options}:</TD> 

<TD>{include file="modules/Product_Options/display_options.tpl" options=$product.product_options options_txt=$product.product_options_txt}</TD>

</TR>



</TABLE>

Usually I'd tinker with it until I got it going, but I don't have that luxury when I'm working a project for business, so I apologize if this has been asked before.