Flash! Nine Justices on Supreme Court Not Constitutional!

According to the U.S. Constitution, Congress has the power to regulate the structure, administration and jurisdiction of the federal courts.  These powers are limited by precepts of due process, equal protection and separation of powers

Having nine justices on the Supreme Court is not in the Constitution, but a simple custom, determined by Congressional vote.  The Constitution allows Congress to change the number of Supreme Court justices if it so deems.  The Judiciary Act of 1789 provided for a six-member Supreme Court with one Chief Justice and five Associate Justices. 

Since the act of 1789, there have been eight more changes to the number of Supreme Court justices, which have varied from a low of five to a high of ten. 

I wonder how many Americans know that!

Consequently, if President Obama wanted to name one or two more justices so that the right-wing activist Gang of Five [Roberts, Alito, Scalia, Kennedy and Thomas]--AKA The Impeachables--could be outvoted or at least stymied, who could stop him, as long as he had enough votes in the Congress? 

Certainly it would be entirely constitutional to change the number of justices on the Supreme Court. It's already been done eight times!