'b' heads flow slightly more,but have huge ports and suffer from low charge velocity and cylinder filling at low revvs and smaller displacments. thus they have lower torque than 99+ 'c' heads.
my personal choice is 'b' heads in spite of the shortcoming. if boosted they are spectacular. note: periodically cleaning the secondary ports reclaims lost flow from carbon deposits. seeing how you already have an early 4v, i'd stick with it. but compare it to a mach1 motor and the differences are apparent.
also navis have larger port which don't match standard tumble port intakes. just a little mismatch.
96 gt. .93 teksid ported 4V, forged, 64mm turbo,sniper tune, BA2600maf, 90/10's, granitelli rear LCA's, 3.90's, QA-1 200in/lb fronts, tubular everything, coil overs.
2011GT, 300A, base model, 3.73, brembos, spoiler delete, candy red. current mods: lethal off road x-pipe, airraid cai, lethal 93 tune, roush axle back mufflers