B will work as you said: SDC to Y and go on the upgrade list. C will be offered but with an upfare to the lowest Y bucket available. I don't believe D will be offered and find it odd that it's apparently sold out in Y but R9. The times I've done SDC with RPU applied, even if R was open on the new flight, I had to still re-apply the RPU after the change ; I didn't confirm right into R.