Hugh Napier's wheelsets have already been regauged to, I assume, FR 597mm gauge. Although it's supposed to be going to Boston Lodge for completion of the new boiler the National Trust previously stopped having built mid-job (which the BBC piece carefully doesn't mention), the regauging doesn't tell you anything about where it's likely to run mostly (the Castle looks like the plan); a 597mm gauge loco will normally run OK on 2' gauge track but a 2' gauge one will tend to fall off 597mm gauge pointwork.