Mumbai: A windfall awaits the dozens of investors, including institutions, funds, individuals and corporates in the upcoming Initial Public Offering (IPO) of the National Stock Exchange.Among the top 10 shareholders selling a portion of their stakes in the country's largest issue yet, public sector banks and insurers, including SBI, Bank of Baroda, General Insurance Corporation of India, The New India Assurance, National Insurance and United India Insurance, are set to rake in substantial gains.SBI is set to mop up over ₹5,000 crore in gains from the sale of 2.47 crore shares in the NSE IPO based on Thursday's price of ₹2,055 in the unlisted market. The country's largest lender's average cost was ₹1.98 croreAgenciesMARKET BONANZA SBI set to make ₹5,000 cr, LIC is sitting on fortune worth ₹54,514 crOther top-selling funds and institutions may receive ₹1,200 crore - 3,100 crore from the share sale. Some of these stakes were purchased in the early 90s at the time of NSE's setting up.Institutional shareholders such as Life Insurance Corporation of India (LIC) and SBI Capital Markets, which are not selling their stakes in the IPOs, are also sitting on eye-popping gains. For instance, LIC's 10.7% stake in NSE could be worth ₹54,514 crore, based on the unlisted share price. This is nearly a tenth of its own market capitalisation of ₹5,44,645.55 crore on Thursday's close.SBI Capital Markets and PI Opportunities Fund I's portions would be worth ₹22,040 crore and ₹11,960 crore, respectively.Individual shareholders also stand to make hefty gains, though these investors are not offering their stakes in the IPO.