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We are not allowed to draft documents for you on this site. But all you need is a standard "equipment" bill of sale.
Here is a simple form you can cut and paste into a document: http://www.free-legal-document.com/bill-of-sale-template.html
Here is more thorough form: http://www.asset-auctions.com/90513/EricssonBillofSale.pdf
You should have the serial number and a short description of the generator on the Bill of Sale.