The more I consider the OSR project, the more I realize why we were able to run Spelljammer when none of us had a copy of the 2nd Edition Rules.
We didn't use any of the optional rules from 2e.
No skills, no endless kits, no player's options, nada. We used the 1e PHB, 1e DMG, 1e MM, MM2, Fiend Folio, 1e Outer Planes, 1e Oriental Adventures and every Spelljammer Monster supplement we could find.
I'm joining a 2e group this month, and it didn't take me long to realize that 2e was *not* what I ran. The only thing from 2e I used was thac0. The only reason I knew about Thac0 was that it appeared for all the Spelljammer monsters.
So, considering the fact that I didn't really use as much of an amalgam as I thought I did, I considered just adding house rules to OSRIC or the AEC for Labryinth Lord. Yet, I redefine thac0, I add a system for creating classes and monsters, my Fighters are different, Thieves/Rogues have tremendous variety in what they can do. Psionics are not the same as 1e or 2e, but are two distinct classes. One is handled like another spellcaster, the other is more like d20 psions. There's an alternate non-vacanian spell casting system. I incorporate some of the Oriental Adventures stuff, especially martial arts styles. Then there's the whole issue of Manueverability Class and how we didn't go from A to E...
There's enough differences that it's a bit more than an add-on to a 1e clone, but nothing like a 2e clone.
So, for now, I'm shooting for a project under the working title of The Odd Omnibus - an Extraordinary Companion for Early Editions. I'm going to write it in a similar vein as the AEC for Labyrinth Lord. It may not be popular, but it will at least be positioned as an add-in instead of Yet Another Retroclone.