IRWIN JACOBS HAS GILLETTE <GS> STAKE Investor Irwin Jacobs said he has an investment in Gillette Co amounting to less than five pct of the consumer products company's stock. Jacobs, who made his comment in response to an enquiry, did not comment further. Yesterday, Gillette rebuffed a takeover proposal from Revlon Inc. Under an agreement between the two companies, Revlon must have the permission of Gillette's board before making an offer to shareholders. The board declined to grant that permission. Gillette has been the topic of takeover speculation for several weeks. Its stock has traded heavily, and arbitragers said they believe Jacobs may not be the only investor who has a sizeable position in the company.