Like many 1st Gen owners, I now run a mildly-built (315hp)1986 roller motor in my 1966 fastback. Of course, the firing order for the 5.0 (13726548) is different from the 289 firing order (15426378). Are there any scavanging / pulse ramifications running a header specifically designed for the 289 firing order on a 5.0 firing order engine, or am I splitting hairs? I swear I hear pulses fighting eachother at 2200 rpm. Or is it that damn Flowmaster 40 drone that's killing me?