Need help with ID Plate and engine Ser #

[oldguy64malibu]

I have a 1964 Malibu convertible, base model.
1. The engine stamping located at the front right corner is F0514J. I think this means it came from Flint Mi. on the 5th month and 14th day. The J I think stands for a 3 speed manual transmission. The engine is a 283 2 barrel carb.
The transmission and steering column now are a Powerglide setup. My guess is that this engine is not the original engine but
wonder how do I find out what exactly this engine is.
The ID Plate on the cowl, firewall, has a grouping of letters & numbers that I cannot figure out. They are as follows,
W 2P S 3C 5W.
2. Is there such a thing as numbers matching engine block and body for the 64 Chevelle ?
Thanks again for all your help.