I'd look for a mount that has tilt and swivel adjustments (example).
That said, to me it seems a bit criminal to attach a TV to those beams, so I'd probably get:
- a nice TV/audio rack (example) and just sit the TV on top of it; or
- a TV stand/console (example) and add a free-standing, adjustable TV mount on top (example).
Oak beams should have no trouble supporting the weight of a 65" TV + mount.