Hi,
I've read thru recent posts (titles mainly), but not found
anything relating directly to my question:

I want to put two beams in the garage strong enough to hang a
shell of a car from.

The shell should weigh in at 1/2 ton max, and I would like to
hang it from the centre of the beam (worst case).

The beam should be run left/right and so the span should be
about 10'

There are no walls to place the beams on, so they will have to
be on posts. I am planning on using the garage walls to prevent
the arrangement from left/right movement, and braceing along the
walls between the posts to prevent forward/backwards movement,
but I plan to lift the car with a chain block at each end, so
there should be no load in either of these directions.

So is there anything inheriently wrong with my plan?

What thickness of wood should I be looking for to support 1/2
ton, centrally from a 10' span?

Cheers
Will