Hi ttodd. I would suggest installing your aux. transmission with rubber pads. As Grigg says it will be quieter and easier on the frame. Here is a picture of how I did mine: http://good-times.webshots.com/photo/2236843520099958186JSAyns

It's a little hard to see, but there is an angle iron bolted to the frame that the rubber pad sits and bolts to. Then the aux. transmission mount has an angle iron that sits and bolts to the rubber pad. There's lots of ways to do it depending on the type of pads you have. But haven't had any trouble with this setup.

Also just a side note. I mounted the aux. trans with the rear yoke right where the carrier bearing used to be. That way you don't have to redo the back half of the driveline, you'll just have to shorten the front half.

Good luck and hope to see some pictures, Paul.

1948 Chevy 6400
1964 Chevy 1/2 Ton