Yeah, I didn't see Core Tapper yet. OH well, so much for my clever Necropolis idea. What YOU guys are missing is that the Reactor doesn't trigger on upkeep, it triggers on having 20 counters, so you guys are worrying needlessly about a few things, most of all that black sorcery which, upon closer examiniation, doesn't faze this combo at all.
Anyway, a Dross Scorpion engine is definitely the way to go. We can tweak the deck around just that now - infinitely untapping the Core Tapper instead of a Power Conduit. We should look into ways to protect the combo... like perhaps Lightning Greaves or something like that to keep the Scorpion and Tappers alive. I still think the Darksteel Forge has potential as a protection piece, we just have to design the deck to get that out easire than hard-casting.
Okay, so here's the combo, clean and simple.
Reactor
Tapper
Scorpion
Ashnod's Altar
Myr Retriever x2
Get cracking people!