Can anyone identify this old RSR chassis?

[John Starkey]

In 1999, Kevin Jeannette bought a much modified, much raced and abused old 911 chassis from Miami and built what he considered to be the ultimate street RSR, with a flat fan engine and "upside down" gearbox. He called it "The Ratt" and a friend of mine has recently bought it and wants to find out where the chassis, which is probably pre-1973, originated. In particular, he would like to find this car's original chassis number. Of course, the number in the front bulkhead had been cut out so that a long range tank could be installed and the production number had also been cut away, to accommodate part of the roll cage.

In the course of my investigations, Jim Torres directed me to John Mason in California, who told me that yes, it was his work, but he'd modified between 20 and 30 chassis in the '70s and '80s! It has very distinctive drilled plates welded in between the A pillars and the rollcage, plus some other rear suspension modifications that John could identify. However, he said that he had not done the drilling in the rocker panels, or made the built up gearshift, those must have been done later.

Any clues, gentlemen?