I think I've sussed it Ron! This was posted by a chap called Gurn on another site:
A letter to J.B. Walker dated September 1952..
"Dear Mr. Walker,
You will be pleased to know that Mark 4 Carp Rods made from materials supplied by you,
have accounted for the following carp in the three months June 16th to September 16th, 1952,
exclusive of fish under 10lb in weight: 10lb8oz, 11lb8oz, 13lb8oz, 16lb4oz, 16lb13oz, 17lb8oz,
18lb8oz, 19lb, 22lb12oz, 24lb12oz, 28lb 10oz, 44lb.
Every rod remains in perfect order without the least sign of strain or set. I am very grateful to you for assistance you gave when we were experimenting with carp rods, which greatly assisted in producing the Mark 4 Rods. It is this
development of modern tackle and methods which has resulted in catches of carp which a few years ago would have been thought impossible, and your share in that development is not small. My friends and I appreciate it very much.
Yours sincerely RICHARD WALKER "
So it looks very much like the tapers in the first edition of RBFA were indeed for an early Mk IV. This would imply that the Mk III that Chris Ball is referring to was built earlier than he thought or that Walker had been toying with the idea of a double built rod before he came up with the compound tapers of the Mk IV
All very interesting. To a few of us at least.......
mg: