Set Label Properties - PDF Why is this so hard?!!!

[rogernem]

I´ve got the following code:

<?php
require('fpdf.php');

$pdf=new FPDF();
$pdf->AddPage();
$pdf->SetFont('Arial','B',16);

$a = 1000;
$b = 2000;
$c = 3000;

$y=10;
for($l=0;$l<10;$l++)
{
    $pdf->MultiCell(60, 10, $a."\n".$b , 1,'C');
    $pdf->SetXY(70,$y);
    $pdf->MultiCell(60, 10, $a."\n".$b , 1,'C');
    $pdf->SetXY(130,$y);
    $pdf->MultiCell(60, 10, $a."\n".$b , 1,'C');
    $y=$y+20;
}
$pdf->Output();
?>

What I need is to generate 30 labels per page (10 rows / 3 columns)
which is already happening and set the labels properties to:
=============================================
Top margin = 1,27cm
side margins = 0,48cm
lable height = 2,54cm
lable width = 6,67cm
Letter (8 1/2 x 11 in)
=============================================
This is not set yet.
How can I do that with my example??!!
Thank you!!