Fitting PYI Flexible Coupling

[BigEasy]

Looked at a few Yanmar engine mount replacement videos;
One nice trick a fellow did in a video was to superglue the bottom washers to the mounting nuts so he could just slide the box wrench with the nut on it into the underside of the supports without trying to squeeze a hand in there.

Yes! I did that also (super glue gel); otherwise, I would have lost a bunch of flat washers & nyloc nuts inside the stringer cavity!
I worked from above the stringer with an electric ratchet & my buddy worked from below the stringer with an offset / angled box end wrench. Problem is that the access hole on the inside surface of the stringer is too small & you can't see what you're doing, have to do it by feel only. To make matters worse, you have to hold the box end wrench at two different angles to blindly capture & engage the backing nut. Very frustrating & time consuming.