Small Block Mopar Engine Date Code 3-4-66

I got the chance to get a complete small block Mopar engine with the Date code of 3-4-66. There are a series of numbers stamped on the drivers side of the block that I do not have as of yet but was interested in asking which cubic inch displacement that this engine may be. I thought it may be a poly block 318 with this date code. It may be a 273? Is the crankshaft on these engines forged? I was wondering if these engines have any value? Any info on the heads would be appreciated. I will try to get as much info on this as I can. I do not want to pull the trigger and buy this if it is not worth it as opposed to a later year block. Engine is complete and has only had intake swapped out to eddy performer. Are there any advantages to an early year date of manufacture small block compared to a later year? The price is very cheap and the block is clean and turns freely. Any advice would be appreciated. Thanks, Tom