Lots of enthusiasm for the idea so far so I feel like a curmudgeon when I say that there is no time saving, just do it all on FB.
Perhaps there are RC/FB pairs which are identical but Ilford MGIV are significantly different in the two forms. Too different for there to be a simple adjustment from one to the other, and when I tried I found I was working it out twice, a significant waste of time.
And there's not really a difference in time to process, not the full cycle--paper out, make the exposure, write it down, develop, swoosh in the stop, dab in the fix (I don't care the image disappears in an hour's time) into a tray of water and then into an empty tray so that I can have a look at it under the light. One minute difference in the developing time just isn't significant. The real time is in staring at the results, imagining how much better it could be and how I could make it happen. The real time saver is in getting it right in four tests rather than six tests, and I think that is better done sticking to the final paper all the way through.
Hywel