Sounds like you made hard work of it. If I recall correctly, when I have done them, I have simply unfastened the sliding clamp, made sure ignition lock off and removed upper column and bush by pulling on the steering wheel using a ratchet strap fixed to the roll bar. After welding the new boss onto the column simply reassemble using new upper column bush (it's same as lower one). You may then have to centralise the steering wheel by moving the universal joint on the splines, but no need to start removing lower columns and pedal boxes.
Incidentally, on my car I didn't remove the steering lock location tube, I simply made sure the upper bush was already on the column when I welded the boss onto the top of it. Doing this means you can have a removable wheel and also retain the steering lock. 😬