got to agree with DH
a stock counterflow 8valve head is just not the place for throttel bodies, and the math just makes it look worse. the firewall gets in the way so you end up with flat faced pancake filters with no ram pipes and sucking hot air that dosen't really work very well, you can feed them from an airbox but then you have just made what is in essance no diffrent to the stock manifold.
if you were to TB it id be unconventional and bring the intake runners right round over the head, makes the induction tract longer and manifold harder to make. but gets the air intake away from that hot hell hole whitch is the back of the engine bay and means ther is room to put proper filters on an not nasty pancake jobbies.
or just meagasuirt it get a prted head and a cam, and enjoy will proably give bigger gains and easyer to live with