I just did the mod on my motor mount and bracket - I used only one bolt though, and will see about adding rubber under the bolt head to prevent it contacting the frame when installed... I'm not sure I'll need it as the rubber of the mount seems to have closed up in the 3/8ths hole after drilling through and holds the bolt in place. To get it out I have to wind it out with an allen key. So hopefully it will never contact the frame. The trick I guess is to NOT drill the hole oversize at all.
Here are some pics of what I used. Note that under the nut (nylock so it won't work loose), I have installed a rubber washer to prevent it feeling like a solid mount when under load.
I also used all stainless steel bits to avoid rust.
I installed the motor mount on my station wagon - what a P.I.T.A. job that was... and I couldn't add any rubber between the mount and the frame, because it interfered with the allignment of the main lower bolt... so I had to just not put any rubber in there and pray that it would be OK.
So I fired it up, and... no rattle from the bolt head hitting the frame so far. I rubber shrinking in the hole I drilled through the mount keeps the bolt in position - evident by the fact I had to wind the bolt in and out. There was no way that bolt was going to be able to just be able to be pushed through the rubber. A good thing!
Loading up the engine against the mount introduces no noise from the nut end, as I have that little rubber washer under the main load washer.
So far so good. We'll see about the real world driving scenario when all this rain stops. At least the car's safe to drive now!