googleSo far, their great wealth has all been on paper. The Forbes list of wealthiest Americans? The Google guys were on it, but we didn’t know when they would actually cash in. Now, Google co-founders Larry Page and Sergey Brin each plan to sell about 7.2 million Google shares as part of an 18-month “diversification” plan, according to a filing with the Securities and Exchange Commission today.

That’ll likely make them real billionaires. The sales would give the two 30-something co-founders $1.220 billion each by mid-2006, but that still assumes Google’s share price stays around Friday’s closing price of $169.4 per share.

Google chief executive Eric Schmidt, meanwhile, will sell 2.2 million shares over 18 months, giving him $373 million — making similar assumptions.

That’s just the beginning. The two founders would retain 81.1 percent of their Google stock holdings, and Schmidt would retain 84.6 percent. The trio would still hold 27 percent of Google’s outstanding shares, and 40.4 percent of the voting power.