On 2007-02-09, Ed wrote:

I don't want to just hang the beam, I want it on top (because I am
removing a wall below and don't want it to show).

Typically the 2x6 ceiling joists would be sitting on the wall top
plates, so it should be a simple matter to sit the 4x12 beam on the
wall top plates so the bottom of the beam is aligned with the bottom
of the ceiling joists. If the issue is that you don't want the beam
to project horizontally the additional 3.5", just cut back the ceiling
joists 3.5" so the beam doesn't project. Be sure that the built-up
posts in the walls supporting the beam are adequate.

the 2x6s are old so they are wider then 1.5 inches, so might
not fit a regular hanger.

No problem, joist hangers are made in a variety of widths, including
sizes for rough lumber.

Cheers, Wayne