The nickle content (strength) was gradually lowered over time as HP numbers decreased. Rated at 185 HP, the block is not the reason its rated as such. The reason for HP ratings is mainly found in the heads with the secondary being the cam.
You could take a set of #16 1968 360 HP GTO heads (incidentally only 330 HP in a Firebird) with a cam swap and have a 360 HP block. The reason pre 71 blocks were so desirable was that the net HP ratings were usually (and actually) off by upwards of 25% , thus the increased nickle in the block to offer a "margin of erro.r"
Would a 73 block suffice at 400 plus HP? absolutely.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
