Our departed friend CAT had a decipher for "MSD", he called it a "Majorly Sh_t_y Device." I don't feel quite that bad about them, but I'm close to it. Accel used to make a far better distributor. Their Pro-Stock dual points were really well thought out and well made. They got bought by Mr. Trashket and that did them in. Now their product is rebadged Mallory product that had already been turned into junk before Mr. Trashket bought them.
My indirect experience with Pertronix has been even worse. Of the 7 buggies in the Buggy Brigade, 5 of them ran one and every one of them had at least one failure. They all carried a spare or the parts to revert to points. I ran a hybrid Toyota/Subaru electronic system very, very much like a D-S II and it never had a problem over the decade plus that I ran it. I know some here are really happy with their Pertronix, but I've not experienced anything really positive about them long term. They seem to be as voltage spike sensitive as the old Mallory Unilights were.
Thank god we no longer have to talk people out of Jacobs.
With a true HEI distributor there are two things that I've seen fail. Module, usually due to poor thermal conductance because of little or no thermal grease. Or simply a cheap one. If the power supply wire is too small for it's length it might starve for voltage and draw more amps than is good for it. Not sure, a guess on my part. 12 ga. is minimum and I think 10 ga. is reasonable.
And the carbon conductor in the cap to the rotor. For some reason those fail more than I'd expect, although I suspect that most of those failures might be attributed to the huge plug gaps that early HEI's had for their spec.
I'm not a fan of the huge HEI cap and I understand that they create a clearance problem in an EB. I am a fan of the "spark-plug" connector used on the HEI & D-S II caps. They're far better than the old socket type of dist. cap connection. I keep forgetting to make note of it's application and/or p/n, but there is a small cap, similar in size to the Ford points cap, that has the spark-plug type connections on it. Someone re-posted it in a recent ignition thread and I failed make note of it. Again.
I'd run a pure D-S II system if the modules currently available were any good, but nothing that I've seen or read leads me to think that they are. Which is why I suggest using the HEI module (particularly one from Performance Distributors) with the D-S II distributor and an E-Core type of coil. All OEM parts, excepting the PD module, with OEM MTBF life-spans.
If you want to spend money on ignition system parts, buy a set of Magnecore spark-plug wires. At least that is money well spent.