Firstly, yea...I suppose the cam could be worn, but I've had 'em last a lot longer than 150k. You actually have an abnormally low mileage car. Especially for being more than 30 years old. For the rough idle, I'd say go through the carbs and ignition systems first. I'd put money on the fault being there.. As for the slow cranking...I'd say your mechanic advanced the timing just a wee bit too much. I say to heck with specifications...put the timing where it runs best and doesn't knock&ping. Somewhere around 10 degrees.....give or take a couple.

The other issue...that light brown stuff in the oil...Yup, that would be water. Could be a slightly blown head gasket...or other treacherous things, or it could just be from condensation. Does it seem to go through antifreeze at all?

I'd say you probably just need to drive it more than a couple miles every day... Get it up to high speeds and high RPMs once a week or so, and that alone might solve all of your problems...

Good luck!
-Matt