I have searched the archives, not find my answer. I need to replace the clutch in my 73 40. I am doing the sm420 swap at the same time.  o I have to use the "3 finger" pressure plate or is there a later style I can get for it?
You need what ever pressure plate is appropriate for the flywheel you are using. If you have a 3sp F flywheel, then you need the 3 finger type. If you want the spring finger type PP, you will need a 4sp or 2F flywheel. You will need an 11 inch (actually 10.75) disk and you may have to grind a little off the circumference to make it a little smaller diameter.