If your's measures 18 1/4", then how did they get 18"? I'll have to dig further into that with them Monday. Something they are telling me is not adding up, but I suspect my head distance is the main culprit.
Yeah, you would think the 600 box would give more clearance being its a smaller box. I don't know what Dynatech has done or is not doing. I'm going to try one more thing, which they suggested. I'm going to unbolt the drivers motor mount and lift the motor a few inches and try to bolt the box in and the header and then slowly lower the motor back down, hoping there won't be any clearance issues. Although, I know there will be. If they aren't able to come up with a solution, then it looks as though I will building a set of headers myself
