Bottom ears are farther apart on Trick Flow heads than on stock heads. The difference is about 0.020 per side. I split the difference so my valve covers fit both. I don't really care about OEM heads but I figure I can't get too far away from that dimension since someone might make a head to OE specs that I do care about.
A little known fact about factory heads is that the valve cover bolt holes are not square to the rail. They are all tipped toward the intake side. Also the rail area where the bolts are drilled are also tipped. This means a flat surfaced valve cover will not sit evenly on a factory cast head. I realize these covers are not directed toward this end of the market, but thought I could pass this along.
Your idea to tip the covers away from the exhaust is a good one. There are cast aluminum covers out there that warp terribly when hot, then go back into shape when cool. Tipping them should prevent some of that issue.
