500557 is a 75-6 400 block casting code. YU for 1977-8 model year is block casting 568557. Possible that 76 overage went into early 1977 and the I (Sept.) is an early casting #. So the block is a 77 block for a 78 model year car.
The 7K3's are good heads..but will only yeild you 8 to 1 with the 400.
The cam will be fine for a low compression motor, but if you decide to go to smaller chamber heads, you should change the cam.
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.
