Those are the same heads as your 434 but with bigger valves. For the bigger valves to have any effect the chamber and blow need to be ported and unshrouded. It would not be a good idea to run those on anything other than a 4" bore motor. The valves will simply be too close to the cylinder wall restricting flow below smaller valve values.
LT1 headed LG4 305 beast! Comp Solid lifter XS-262-10S, 1.6 Roller Rockers, 10.2:1, Holley 4160 600cfm, modded Weiand 7502 intake to fit LT1 heads____ Custom cylinder head cooling. Weiand 8208 Short Water Pump____TH-350 3 series 3.73 with 2 series posi and spacer____ Hedman Hedders 1 5/8 headers and Y-pipe 3in Exhaust, Dynomax 3" Bullet muffler ____Moroso Ultra 40 Wires ACCEL HEI Super Coil ____Competition Engineering 3120 Bolt-on SFC's____Homemade: Wonderbar, solid tie rod sleeves, Aluminum LCA and Panhard Rod with spherical rod ends, alternator and PS bracket, Strut tower brace, and Decoupling torque arm with telescoping link.
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-- President George W. Bush
During a photo-op with Congressional leaders on 12/18/2000.