I went through the same thing and am glad I did. I detected an oil leak in the pan gasket by running the engine on a test stand before installing it in the car. I made the stand from a few steel angles and plates. However, I went a little crazy and equipped it with instrumentation and even a Mustang ignition switch to start the engine. If I have any pics scanned in the computer, I could e-mail them to you if you want to see what it looks like. My wife claimed that the car could have been finished way sooner if I hadn't spent so much time on the engine test stand.

 

I've thought about doing the same thing after seeing a few at swap meets. "Wanna hear the engine run before you buy it? No problem."
Here is a commercial version Mighty Mount
All the ones I have seen were homemade, along the same lines. I figure that if I were to start building one, I'd just flip a junk engine upside down and build the frame to fit. No plans needed that way. Take it off the engine, flip it upright, and add the radiator support and whatever else.