I'll chuck in some of my experiance with this matter:
If you don't have a heavy weight balancer plate, use a rear drum by all means but BEFORE you mount the rim to the drum, spin up the drum first. You might be surprised that the bare drum is out of balance.
Next balance a front drum but I couldn't find anyone who could do so with the rim and tyre fitted. So we mounted the front drums using a small Japanese car sized alloy wheel adapter, (take the wheel bearings out), spun them up and noted any balance discrepancy. Mark the drum balance spot using a small piece if masking tape so you know where to align the rim and add any weights required.
Now you know if your drums are out of balance and you can weight the rim accordingly after you spin them up using the rear drums. Carefully add the weights as required.
It's all very time consuming but it was the only way I could finally achieve a good (read great!!), balance on my wheels. Well worth it in the end but I'm not looking forward to when I have to buy new tyres!!! Got to go through all the motions again....
