well i know that my eddy heads hang off the block a bit more than an iron head and in turn push the exhaust out about 1/4 or so, that may be the issue that comes into play with a 4 speed?
I have stock headed 340-360's in both cars. The z bar tags the tube almost dead nuts at 12 o'clock on both cars. It would have required a bend of nearly 3/4 to 1" in order to clear.
As far as ground clearance, you can't beat Dougs or tti.
From a power perspective, tti and dougs are not the best choice.
Everything in these things is a trade off. You have to choose which you want. Max power = limited ground clearance, just the way it is. This isn't the thread for my 25-40 hp gain from only a header change from tti's... 8)