Thought I'd share a few photos on the difference in distributors between a '75 TD427 and a mid 80's BBC distributor. My findings is that the LENGTHS are identical. The reason a regular ol HEI won't simply drop in a tall deck is due to the oil pump drive as mentioned above.
The medium duty truck's 427 distributor housing is cast iron. It has no wear a'tall.
If a guy really wanted to, he could grind the rivets from the TD427 gear and then grind the drive tab off the HEI shaft and fasten the TD427 gear by either re-riveting or roll pin. If a guy wanted to...
on edit: Found some n.o.s. Blue Streak parts and they're on the way. Cap, points, condenser, rotor and coil. Sometimes ebay works out for the better.
BTW Echlin is now Standard Motor Products stuff (bought out) SMP still does the Blue Streak line but Echlin is the lower line SMP. (as per NAPA counter guy)