<VV> steering column interchangeability

[Neal]

Hi, I'm working on a 65 with the long steering box shaft(box to horn button).
I have a telescopic column that looks like it is out of a 66 or later. I
planned on changing the steering box out with one of the "flaming river" quick
ratio boxes that has the very short shaft (67-69). I realize I will be
required to figure out the length of shaft needed with appropriate couplers.
My biggest concern is the differences in the firewall where the column base
attaches. Anyone been down this road? Thanks Neal