That is true if you are looking at peak power. The top end of the engine determines the peak power capability, the bottom end determines the RPM range. TF240 heads will make roughly the same power on any size shortblock with the same compression. The difference will be the RPM where the power peaks. If the OP wants to stay with 4.88 gears then a 451 inch shortblock might be the best choice. Peak power would be the same, torque will be down and 7200 rpm shouldn't be an issue. At this point it seems cheaper to change gears than to change the rotating assembly but there could be other factors. Some people like high winding engines. I think it is cheaper to build power with inches and keep the RPM down so the valvetrain isn't constantly getting buzzed.
