It is not clear to me how
or if this locomotive was returned to service using the FRA standards for a new/rebuilt locomotive boiler are not? If it was, with intent that the locomotive would or could potentially operate on a FRA regulated railroad, FRA would have had some initial involvement from the start. This is how Mr. Taylor and others at the CRRM handled and coordinated with FRA regarding RGS 20 and it's occasional use on a FRA regulated railroad. Same with the Eureka No. 4.
Based on the varied information posted, that does not sound like the case here.
MD Ramsey