I'm getting ready to do just that, use a 400 bellhousing on a 460. On my first attempt I found there is a depth difference, took it all back apart, and left it for a couple of years due to other projects. Since I have found that you can use spacers and make it work but I do not have any measurments made or materials selected. I need to mate them back up and see how much space there is first. I'm open to ideas and suggestions if anyone already has this info...