After some looking and sorting it would appear that there is Pertronix, and this one from Mallory:
http://www.speedwaymotors.com/Mallory-Ignition-4518001-49-62-Chevy-6-Cylinder-Electronic-Distributor,6904.html
I also found one other, that states no iron distributors with mechanical advance:
http://www.hot-spark.com/1-3DEL6V1.htm
Why is not clear. So you have some choices.
1, Modify a GM HEI,
2, Pertronix,
3, Spend big dollars (400 for the Mallory)
4, Use points
5, Take a chance with the "Hot Spark" thing.

Questions that come to mind. 1, Looks, you get to work that one. 2, Reliability, That should open the flood gates. 3, Availability, Stock parts can be bought at FLAPS, Proprietary can only be bought from the manufacture. Includes, Pertronix, Mallory, And Hot Spark. So in conclusion?
Opinion coming, Points are reliable and available. Looks, I like the stock dizzy. The Mallory is good looking as well, but at 400 dollars it ain't that good looking. Performance, Would I even notice if the best of these gave me 2, or 3 horsepower? Uh...no. With a modified engine, maybe. For me and me alone, I will keep my points. Your truck you decide. And on the HEI v. Pointless argument? HEI is a magnetic pickup. Mallory is a magnetic pick up. Pertronix is a magnetic pick up. Advantage to the HEI? Coil is in the cap. No loss from a lead. If I wrong, and I have been lots of times show me. I like to learn.

Steve H