Stuart,
You were not dreaming. Earlier this evening, after reading what I wrote above, I checked the 1954 Shop Manual and it shows the distributor set-up as you describe - they most likely were using an older photo (they do this in a few places in the 1954 Operator's Manual, too).
After loking at the 1954 Shop Manual, I checked my supply of 1954 distributors and three out of four are as I described and one is as you describe (maybe it had also been converted to eliminate the slotted round-nut and the post that was threaded only on one end).
This discussion shows, once again, that pictures are better than words; and, many things might have been changed at any time over the 50+ years that these trucks have been in service.
Greg (54cabover), if I can find one more spare post/spacers/nuts for the distributor, I will let you know (I took them out of two distributors when I installed Pertronix ignitions and I will have remember where I hid them for safe keeping). I think it is possible that this type of post was used on 235/261 distributors from 1954(?) to 1962 (I found it also on a 1960, 261).
Tim
