I would get the FastenR-T1 and definately would not just hang the camera by the manfrotto d-ring! I'm a mechanical engineer so I understand that if it wasn't designed for it, then it is probably not safe to hang expensive camera gear from it...
@icanon - I'd love to see some pictures of your DIY version...
@rick - I believe you can get the lowepro toploader pro cases to hold a 70-200 L IS II with hood. Not specifically designed to be chest carried, but some come with the harness. Mine will hold a mounted 70-200 F4 L IS with hood...seems like there would be lots of extra space for the larger F2.8 version as well.
Stephen