A couple of thoughts related to the original post.
Firstly I have a copy of a page produced by Bill Button in the states about his conversion of a 1960's +4 to a Gemmer box. He uses a TR7 upper column and a Jag XJ6 steering rod connected with an MGB universal joint. A big hammer is used to adjust the inner wing!
Secondly if the concern is just about the long column, wasn't the early +8 steering box the same as the early +4 but with a split column. I bought one from a Miscellany ad a while ago because at some point in the future I wish to upgrade the steering on my 1966 +4
