I had good luck so far. I also filled up the water jackets half way with hard block. It dosn't do squat for the bottom end, but it helps keep the cilinder walls from distorting.
Why are you going with the gt-40? that will be a huge restriction with the canfields even if it is ported.
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79 hatch w/ NA 347,stage 2 Canfield heads, out of the box Victor 5.0 intake, solid roller cam, Aeromotive fuel system, proshifted TKO II.MY CAR
http://www.mustangworks.com/cgi-bin/...splay.cgi?1288
93lx all stock + tremec