I've not tackled a cement bubble before (I didn't buy a set from the previous run(s) as I didn't know if any were preserved), so once I get one in front of me I'll be able to see what kind of a re-gauge bodge is possible.
If it's just pinpoint axles, I can obtain plenty from the Scalefour Society stores.
If the IRM original axles are already the standard 28mm length, then it might be possible to do as I did with the "A" class, i.e. remove the IRM wheels and wang on the P4-profile ones then reassemble.