
I have no doubt that Ed used a Mighty Mite clone of a Dimarzio Super Distortion on that first Van Halen record (in the Franky that is). My 'new' (2011) DSD just totally reeks of that first album. There is a push and warmth to the mids/upper mids along with a presency 'sheen' to everything. The gain and aggressiveness is there as well, which goes missing in my 'Custom Custom' (same 14kish type wind, but uses an alnico2). The palm mutes also have more of that 'peaked' type charector as well (DSD). My 9k stewmac sounds very 1978ish as soon as I put an alnico 2 bar in it. The a5 bar that came in it sounded very '59ish (thinner, brighter).
A 'possible' scenario, concerning Seymour,
I think that maybe Seymour had talked a bit with Ed, and that Ed had disclosed (probably had the Franky right there with him) that he was using a Mighty Mite pu (1300). Seymour actually worked for Mighty Mite and had designed thier line, so he knew EXACTLY what pu Ed had (MM 1300). Ed, possibly told him that he liked the sound of the pu's in his (Es-335 ?) but thought they were a bit weak when he put them in his strat. Seymour then, probably thought "Well, I can just rewind the pu a tad bit hotter to give it a little more mids and push". I think that the Duncan '78 is probably based as closely as possible to that. The 'EVH Custom' that Seymour was selling by '79 (Basically an SH-5) was Seymours take on the previous DSD rip off that he designed/made for Mighty Mite, which he knew for a fact that Ed used on that first Van Halen album ('cause it was probably in Ed's Franky when he first came to Seymour, in early '78).
I mean, like Pete's clips show, a 14k ceramic magnet (specifically hex poled) has OBVIOUS Vh1 mojo, while a 9k alnico 2 pickup gets you the '78 tour tone up through VhII tone.