48 'B's is far too small a figure, you've left no room fo training and support/attrition airframes at all. 70FAA/70RAF is a much more realistic level, as these aircraft will have to last us decades.
And as LockMart have been saying for at least a decade now, if you want A's with probes for refuelling, you just have to ask! the cockpits for all three models are identical, the A has the space for probe left empty and as for aerodynamic testing, in flight it's identical to the B so it's been done. Any extra costs to certify such a mod are going to be a lot less than spending big bucks on new tanking equipment for the RAF's fleet and the associated training and logistic pipelines.