Randall, motor plate or traditional frame mounts? I know this doesn't answer all of your question but it's something to take into consideration.
If using the traditional mounts, there are two common sizes. They vary not only in height but width.
If you're going to do the traditional mounts, Elston makes a great mount that allows you to position the engine exactly where you want it.
http://elstonheaders.com/page6.html