I'll see if I can get a measurement......but I initially cut it off right at the base of the worm gear....after inspecting and pontificating on stuff for a while, I ended up cutting it about an inch higher to make sure I had nothing but clean shaft to work with (I didn't want any remaining pieces of the worm gear left attached). I cut it where the screwdriver indicates....
Now if you are asking about the outer 'column' that the steering shaft goes through, I'll need to get a measurement....I cut something between 2-3" off....if you use a shaft collar to hold the bushing in place, you can cut it a bit shorter without issue. If you use the ujoint to hold it in place, then you don't have as much margin for error.
If I did this project again, I would consider not 'turning down' the end of the shaft from the OEM 15/16" or so to the recommended 7/8", and instead I would have tried to open up the inside of the bronze AA bushing from 7/8" to 15/16" (or whatever is needed to slip fit over the shaft.) The big advantage to this (in my untested opinion) would be the option to grind 2 'flats' on the end of the steering shaft and use a 1" DD ujoint instead of the 7/8" round. I know 15/16" is NOT 1", but I think I would have been comfortable with that fit. Once I turned things down to 7/8, I wasn't comfortable trying to fit into a 1"DD joint, and turning all the way down to 3/4" DD worried me that the flats would grind into the hollow center section (or at least the wall would be VERY thin). Maybe that doesn't even make sense with how I am trying to explain. In the end, I followed the AA plan, turned it down to 7/8, used their bushing as is, and used a 7/8 round joint on one end (and 1"DD on the other).
Not sure I understand exactly what you are saying, but here is a pic of my set-up with a power power box in the mount. As you can see, the splined input for the power box is almost exactly the same as the manual box - just in front of the cross member. The manual box looks to have a long input shaft, but it is pretty much the same length, it just 'sticks out' farther as the box housing is much less massive. If one wanted to only use a manual box, it is possible to push the front end of the box a couple inches further forward (the nose of the manual box is shorter than the power box), and that would essentially put most of the ujoint in front of the cross-member as well. The downside of this is that any angle to the lower steering shaft would have to be accommodated inside the pass through, whereas with the joint inside the pass-through, its easier to accommodate any shaft angles.
I definitely made the pass through hole bigger and higher up into the cross-member.
I pulled my steering wheel many years ago without a puller - I recall it was a PITA and its easy to damage the wheel. This time, I used a large bearing splitter that I had sitting around (probably the large HF one), put the splitter piece on 'backwards' or reversed so the flat section was against the bottom of the wheel (center hole has to be big enough to fit around the column) and screwed the drive screw down against a socket or thick washer on top of the splined shaft. Maybe because I got that thing off years ago, it wasn't particularly tight.