In theory, you can't do it, but in practice you can do it in ways that will probably get you close enough that you won't be able to tell the difference. You will have definitely have to align them left/right, but it shouldn't require any stretch/shrink. If you have the R4's, I say go for it and make it work.
Just record to the two R4's and see if they line up. I've taken sources from 2 UA-5's before and the clocks matched well enough that you didn't need to stretch/shrink either of them, just line them up. In, fact I've seen this a few times with different UA-5's. It's simply that the manufacturing tolerances on the clocks are "close enough".
If that isn't close enough try this:
- Take your 2 R4's you recorded to separately... arbitrarily call one of them the Master "A", and the other B.
- Take the files from A and copy to your computer.
- Set up a digi-patch from B to A, and dub real time from one to the other. You will have to do this twice, once for channels 1/2, and once for channels 3/4
- Since the R4 resamples, even if the clock on B is different from A, it will resample it, and it should match what it was when it did the initial recordings on A.
- now take the new "dubbed files" from A and they should match with B time clock wise.
- What this really depends on is that the clock on B will play back at the same rate it recorded (which it should), and that A will record at the same rate twice in a row (which it should).
I have recorded Mics > R4, and SBD > R-09 before... when you pull up the two tracks they are off 300ms/hour. So I patched R-09 > ODL276a > R4 and it was within 2ms/hour... close enough for me.