360 magnum engine,stock serpentine belt system with motor plate???

Well I might of found a 75 dart sport that was built to be a race car. It's set up with a big block right now, but the owner will sell it as a roller. OK I don't know if I would have a small problem or not? What I am talking about is the car has been set up with a Mustang II front-end. Instead of trying to weld motor mounts on the frame. I think it would just be easier to run a motor plate like the big block used. My question and concern is if I do, will i run into problems trying to run the factory serpentine belt system? If I get a plate it will be from A/R engineering and is 3/8 thick