We seem to be at cross purposes
There never was a McLaren M3B
What people call an M1C is what was also known as a Mk3. This was a Can-Am sportscar model, one of which was 40-10
Likewise the M1B is the same as a Mk2. But the M2A and M2B were single-seaters
The M3A was also a single-seater, of which three were built. There were 25 M1Cs (or Mk3s)
Well, you apparently know more about my car than I do and I am pretty familiar with McLaren history and the cars of the period. I was caused to endlessly enter the car with a different designation than M1C, because the FIA among some others saw the car had major differences from its sisters in the series, and the factory put them there. The car was not a single seater.
The American Mk3 designation did not properly fit as 40-10 was built, at Trojan, with some very different bits and bobs. They know the car, have acknowedged it, helped with the FIA certification - and the late John Collins, the chap who actually first assembled the car while working at Trojan, always made the distinction as he knew the car intimately in that our race stable was about 20 feet from his shop for many years.
So what would you like to call it? M1C ? M1C/b ?, Mk3 ?, Mk3/b ? M3b ? There were two built in this configuration and Trojan did it subsequent to the 1967 season. That I do know.
By the way, I saw and sat in 40-11 in Sweden about 15 years ago. It was in green and yellow livery and was being campaigned in the Steigenberger series at that time. I hope that would be of some help in locating it as I noted in one of the postings above that it was 'unable to locate'. I may even have some photos somewhere.