You may not have to balance that clutch
I replaced the clutch in my 1939 Oldsmobile a few months ago, and now the engine vibrates at around 1200 rpm. It dissipates a little as I speed up, but it does not go away. I asked a mechanic friend about it and he reckons it is because I didn’t balance the clutch before putting it in. Does that mean I have to go to all the trouble of taking the clutch back out to have it balanced? I don’t want to do that if it isn’t necessary.
You are most likely not going to need to go to that much trouble. Get under the car and take the inspection pan off of the bell housing. Undo one of the bolts holding the pressure plate assembly to the flywheel, find a slightly longer bolt of the same hardness (never use ordinary hardware store bolts on a clutch) and put a washer or two under the bolt and torque it into place according to specs. Now take the car out for a spin and see if the vibration is better or worse. If it is worse, put the original bolt back in and then install the longer bolt and washer across from where you installed it originally.
Take the car out for a run again. If the vibration is better but not completely gone, add another washer to the bolt and test the car again. By playing around with the bolts and washers you should be able to eliminate your problem. This trick works fine on vintage production cars from years ago, but if you had the same problem on a modern high-revving racing engine, you would want to have everything balanced, including the crankshaft, rods, pistons, flywheel and clutch, but that isn’t necessary on a 1939 Oldsmobile.