Robert,
Don't feel too bad.
Many of us have been in the same position.
The rotor head can be rebuilt, provided there's no serious corrosion.
Ken Brock Manufacturing can take care of that. They can also rebuild the stick assy., since it's one of theirs.
You can get the frame materials from
Wicks Aircraft, and new AN hardware to bolt it together.
The problem you'll find trying to rebuild something like that is that you don't know how well the builder drilled everything out. You may drill out a perfect frame, and then find that the secondary structures won't match the new frame (boom won't align with the holes, or the axle blocks won't fit, etc.).
Then again, if it was assembled from the Bensen
kit (predrilled, precut), the chances are good that replacement pieces will fall into place. But you won't know until you take it apart, and compare hole placement with a set of plans.
This probably isn't what you want to hear. Sorry, but I've been there.
The Mac engine can be rebuilt to run very well, and to have a long life. Ron Herron ran one for years on his Bensen and then mounted it on his first Little Wing. With a good rebuild and one of Rick Whittridge's CDI conversions, it'll have good power and reliability. I have one of his CDI's, and it has made a world of difference.
Hope this helps.