Very cool, thanks for doing it!
Was going to come and say the numbers might be better in stereo simply due to old componentry and/or the L/R gains being separate, as one channel suffering could bring the bridged number down. But as usual you had it covered.
My buddy will still roll his 89 Mustang LX to SQ comps running two Class A 6.0 and one 3.0. Even painted the car SS blue to match when he first did the install way back when. Great stuff.