What the OP has is correct. Since the m/c he has has four studs it is a cast iron stock style. Now he needs the correct m/c backing plate for manual brakes - it will have a round hole instead of the wierd-shaped one.

Those studs are what help secure the pedals to the firewal - so they are necessary. While it is "uncomfotable" to install, its not a big deal. The studs are accessible inside the car to install the nuts.

There is no adapter required for this unit - only needed for the late model aluminum 2-bolt m/c's