Build Your Own SLA/SLS

This is seriously a nice mod. Good job!

http://www.bcmagnets.com/products/magne ... sal-joint/

cheap and easy

I'm not using them on a printer. I use them for another application as a universal joint with zero slop. The smallest ones you can find will be more than strong enough to hold a projector, even from a ceiling. (assuming you are using 3 or 4 of them)

There is an alternative source, but quite expensive. https://www.thorlabs.com/newgrouppage9. ... up_id=1546

You might get ideas from looking closely at the photos for a nice implementation with a few $1.50 neodymium magnets.
As far as your statement about them needing to be fairly low.. No one says you need to place them under your projector. You could put them on the side and have them stick downward toward their own bases mounted to the side.