What Have I Got?

273 destined for a '64 Dart GT that currently has a /6 in it.

Engine number: B273-1-10 with 8132 in larger numbers below that.
Heads: 26568920 on both heads with 1046 on the drivers side and 1056 on the passenger's.

Questions:

When was it built?
Which car was it built for?
Where can I find OEM part numbers for engine components (i.e. distributor)?

I need this stuff to be able to figure out which engine parts to order and whether these heads are stock to 1964 or something else.

Thanks for your response.