I read in a magazine a couple of years ago of a company that was making "modular bellhousings".
In short, pick the engine you want to use, and the tranny. They would provide "rings" to meet each application. Then there were "spacer rings" to fill in the distance between the first two pieces. Seemed and looked like a very simple idea, well executed.
Does anyone recall which company?
Thnx, Mikey Bynum