That's it. Still need to align, and maybe shrink/stretch as they do not share clock. Its just that doing so is made easier because the channels from both recorders that share identical signals are used to do the alignment. The waveforms match each other precisely so they are easy to match up. Besides making it easier it also allows for close to perfect alignment, preserving the phase relationships.
When I did it I was playing around with extending my standard 4 channel baffled omni setup (Left/Center/Right/Back) by adding a fig-8 coincident with the Center omni to form a Mid/Side pair. I needed the second DR2d to record the figure-8 Side channel. I used the Center omni (Mid) channel as the common signal sent to both recorders. In that way I was assured that my standard 4 omni recording to the first recorder would not be compromised in any way, and that having both Mid and Side channels on the second recorder would preserve the critical phase-relationship between that pair. If for any reason I couldn't achieve absolutely perfect sync, any time smear would manifest only between the other omnis and the M/S pair.
As it was it lined up near perfectly and required no stretching (~hr long classical performance). I could have done a null test to confirm sync, inverting one copy to see how closely the two cancel out, which would be a good check if I did this regularly, but I didn't bother since that was unnecessary for the purpose of my test.