best bet is to try and get a MSD Boost Timing Master box.It will retard the timing 1,2 or 3 degrees per pound of boost you want to run.
The stock HEI esc system leaves a lot to be desired but if it is working then use it.
I have a HYE Tech plenum and had to modify the bracket to push the TR6 more rearward as it would not sit flush on the plenum.
Bob probably didn't have every single brand of plenum to test fit.
SIngle best product I have installed on my engine!!!!!!!!!