i know the photo you mean of that Ernie Ball set - i think open-g posted it? - but i haven't found it yet.
i did find this, posted by Toru A on page 3 of the "Keith's Other Teles" thread - [
www.iorr.org] :
>> Micawber is a 1952 butterscotch-coloured model with a black pickguard & a stock 3 way switch.
The sixth string is removed, it's always tuned to open G, with the following gauges: .011, .015, .018, .030, .042.
It has replacement tuners & a brass replacement bridge with individual saddles,
and the nut is cut to accommodate 5 strings-they aren't evenly spaced across the fingerboard,
but the first string is moved a bit to keep it from going over the edge. <<
i don't know who Toru A was quoting there, or how authoritative they are.
i also think the gauge Keith uses varies depending on what era you're asking about;
and there's an interview around here somewhere from the 1980s where his guitar guy talks about
changing to heavier strings sometimes to keep Keith's hands strong.