Here's a simple balance checking fixture we made, just something to quickly verify flywheel and PP balance without sending the parts out. We used materials we already had on the rack, basically angle iron and some 1" dia cold rolled shafting. It turns out this fixture works pretty good for what it is, as it detects an an out of balance 2 grams on a 6" radius. The arbor was made by turning an appropriately sized hub and then using red loctite to fix it onto a section of cold rolled shaft...

DIY Flywheel / Clutch Balancing Fixture

Here you can see that one end of the support shafts non-adjustable, just holes for the pins that are threaded into the shafts...

Here you see the other end of the support shafts, which go into slotted holes with adjustment screws to allow adjustment for parallel of the support shafts...

Here you can see this old iron flywheel, supposedly neutral balanced originally, required 43 grams applied to it's rim to achieve neutral balance. Since the parts balanced here were iron/steel, magnets made it easy to temporarily attach and move around weights...

Below is a steel flywheel I had been using on my 355. I had taken a little weight out of the backside a year or so ago, it took about 12g when checked to balance it out. With the flywheel zero'd out, I then bolted the Ram pressure plate on to check it's balance. Turns out it needed 22g. I then rotated the PP 180 degrees on the flywheel and checked it again to verify. Took the same 22g on a 5-1/8" radius in the same "6" location. Looks like depending on how the two were bolted up before, balance of this assembly could have been out a minimum of 10g or a maximum of 34g overall. In this case I was lucky that the weight that needed to be added just happened to line-up with an existing bolt hole, so I just made a weight that slipped over a longer stud in the flywheel's #3 position...

This dual friction disc we had laying around was only out 1g @ ~ 5"...

When we set the fixture up on the concrete floor instead of the bench plate, resolution improved to 1g with these cold rolled shafts. Turns our 65lb bench plate that we were using for the pictures plugs into a single 2" square receiver style socket in the bench, it turns out the bench plate moved a little when the parts were rolled from one side of the fixture to the other.

Here's some pics with an old cast flywheel i had laying around, here you can see some leveling screws installed in the base.

We also made some different arbors so we could check balance on different clutch discs, with different arbors the fixture could also be used to check balance on brake rotors...