The side sill refers to the frame. Typical locations for EMD builder plates are centered below the cab on the sill, on both sides. My prototype had no SW1000s, but did have SW1500s which had essentially the same details for a number of items , including the builder's plates. They are visible on one unit here (engineer's side) http://www.wplives.org/collectionpageimages/locomotiveimages/wp1503_a.jpg and here (fireman's side) http://www.wplives.org/collectionpageimages/locomotiveimages/WP1503_b.jpg.
The Loco Photos site will give you many images of SW1000s for these and other details http://www.locophotos.com/Search.php . Scroll down to "select locomotive model" and choose SW1000 from the drop-down list EMD section.
Rob Spangler
EMD's builder plates were located on the side sill below the cab.
Try Microscale MC-4056.
http://www.microscale.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MC-4056&Category_Code=PLATES&Product_Count=0
Second row is the older style EMD builders plate.
Chris van der Heide
My Algoma Central Railway Modeling Blog