After a bit more work, which involved cutting off the mounting unit at the end of the column tube, setting it all back up, marking for length, cutting the column tube, and then putting the mounting flange in to primer, here's the near-finished result.
I have two steering shafts out of 60 series trucks - interestingly they are very different in length. One happens to be pretty much the right length to fit into the shortened column tube. Al I need to do now is cut off the yoke fitting on the end of the shaft and weld in the end of a 40 column shaft with the coupling on the end. I will wait until my power steering gearbox gets here (in transit now) before messing around with that.
I have thought a lot about the steering system to use. While the 60 series set up is definitely a simpler and more robust arrangement, I just would rather not cut into the shock tower and fender to fit it in, or, alternatively, cut off the rivets and remove the shock tower and put on a #ord shock tower.
Problem was, I want power steering, and 40 series power steering gearboxes are very spendy indeed. I tried to get one on ebay a couple of times, but there was always someone wiling to spend more than me. I was just about at the point of giving up on the power steering and settling on manual (if only for the interim), or accepting the compromises and putting the 60 series stuff in, when something new showed up on Ebay: a 2000 Bandierante (Brazillian version of a 40 series) power steering box and pedestal, with only 10,000 or so on it. TLC in California was selling it, and said that it would bolt right into position - well, we'll see when we get it I suppose. I managed to win the item for a pretty reasonable price, and it should show up in the next 6~7 days.