Piston ring indexer?

I am getting ready to assemble my engine and need to file fit the rings. Can someone put me on to a good ring-squaring tool for a 273 + .040 bore so I can check end gap? Saw the roll of tape idea and the $50 one on summit, just looking for options.
TIA-DR:coffee2:

If the pistons are flat tops, just use one of them upside down. That's what I do.