I have come up with a solution
1. changed the columns size and added and extra column in line 60 of rep107:
$cols = array(4, 60, 195, 260, 285, 325, 390, 450, 515);
2. added the Gross amount calcuations ( hardcoded tax multiplier in file, but works for me for now) in rep107 as per below from line 114 onwards:
$DisplayPrice = number_format2($myrow2["unit_price"],$dec);
$DisplayQty = number_format2($sign*$myrow2["quantity"],get_qty_dec($myrow2['stock_id']));
$DisplayNet = number_format2($Net,$dec);
//Calculate Gross number
$DisplayGross = number_format2($Net*1.16,$dec);
if ($myrow2["discount_percent"]==0)
$DisplayDiscount ="";
else
$DisplayDiscount = number_format2($myrow2["discount_percent"]*100,user_percent_dec()) . "%";
$rep->TextCol(0, 1, $myrow2['stock_id'], -2);
$oldrow = $rep->row;
$rep->TextColLines(1, 2, $myrow2['StockDescription'], -2);
$newrow = $rep->row;
$rep->row = $oldrow;
if ($Net != 0.0 || !is_service($myrow2['mb_flag']) || !isset($no_zero_lines_amount) || $no_zero_lines_amount == 0)
{
$rep->TextCol(2, 3, $DisplayQty, -2);
$rep->TextCol(3, 4, $myrow2['units'], -2);
$rep->TextCol(4, 5, $DisplayPrice, -2);
$rep->TextCol(5, 6, $DisplayDiscount, -2);
$rep->TextCol(6, 7, $DisplayNet, -2);
//Display Gross Number
$rep->TextCol(7, 8, $DisplayGross, -2);
3. Change the row descriptions in doctext.inc line 30
// default item column headers
$this->headers = array(_("Item Code"), _("Item Description"), _("Quantity"),
_("Unit"), _("Price"), _("Discount %"), _("Net"), _("Gross"));