If I understand your question, you want to build up a torque monster engine to put into the Eldo. Is that right?
May I ask why you want to put in a different engine, when you already have an engine in there that can pull a freight train up a steep grade
However, if you want to pursue that course of action, can I have your 500?
I love those engines! Lighter than a BBC, more torque in stock form than dam near anything else, and by simply changing intake manifold and exhaust (Have you ever seen such an intake design?) you can wake it up even more!
Just don't try to rev it - Cad motors have a valve train that is reputed to give grief starting at about 4500 rpm.