As Patrick said, look for the cross bolts (bolt heads) there'll be three of them on each side of the block just above the
oil pan rail. If the engine's in the car, jack it up and you should be able to see it from underneath. This'll just indicate whether it's a 427 (could be side oiler or top oiler). Heck it could even be an "cross-bolt" aftermarket mod to a 390 or such too.
Dave