Julian I will attempt to explain
The original and most copies of the original (Safir Spares, John Wisher, etc) bell housing use a small 148 tooth flywheel. This is good as the engine is low in the chassis, it decreases the amount of flywheel and housing hanging below the chassis. Flywheels to fit are harder to find, and in my case even harder as I want a zero or neutral balance flywheel. Kennedy engineered products make what is essentially a Pantera bell housing that is drilled for the gt-40 orientation. It uses a 163 tooth flywheel resulting in more flywheel and housing hanging below the chassis. The ZFQ uses very common late model 5.0 157 tooth flywheel which has huge aftermarket support from the mustang crowd. Easy to find zero balance, multi disc, etc at reasonable cost. Cosmetically the Kennedy is casted without the strengthening ribs. The only other 157 tooth compatible bell housing is the quick time which is all steel and also without the ribs. So for me the best compromise in appearance, size, and use of easily available parts is the ZFQ