Shares of Square parent Block Inc. are heading higher Monday, building on Friday’s record rally, after an analyst at BMO Capital Markets said he saw further upside for for the payment-technology stock. BMO Capital Markets analyst James Fotheringham upgraded Block shares SQ, +6.41% to outperform from market perform late Sunday, writing that their valuation looks attractive following a sharp drop in multiples across the payments industry. While Block shares rocketed 26% in Friday’s session to log their largest single-day percentage gain on record, and up about 5% further in Monday trading, the stock is off 55% from its August closing high. The company’s forward price-to-earnings multiple had come down 70% over the past year as of the writing of Fotheringham’s note. “We view this as a rare GA