Need some info - "318-3" engine

ok, from what I've read, the early truck 318 engines designated "318-3" on the block casting had a forged, hardened crankshaft...

I just picked up a 318 that is supposedly the original engine out of a 73 Cuda. This block is also showing the "318-3" casting number on the side. Any one have any info on these blocks? Is the 318-3 designation significant in the newer engines?

I just picked it up last night, so I haven't had time to even get the full casting number, but the -3 stuck out when I was loading the engine up...

TIA

-Alan