12AU7 Gain Question

I recently purchased (3) 12AU7LG tubes. Two for my PS Audio BHK pre amp, and one as the input for my tube amp. The tubes were selected by the seller based on my equipment, and have different gain.

2 pre amp tubes are Mu A=16 and B=16

1 power amp tube is MU A=2016 and B=16

Ok, so I'm a dummy, and although the boxes were marked as such, I mixed the 3 tubes up, and they all look exactly the same.

Question is, can I use a multi meter on the tube pins to test the gain difference? How can I identify the odd power tube?

Do I need a tube tester?

Can I just keep rotating the tubes to try to find a gain in DBs in the room, or channel?

Thanks Mark O