I am much more involved in the work plan to get 1630 running.
In broad terms 428 is undergoing a complete mechanical rebuild. Many of the worn or damaged parts have been fabricated or repaired. However all wheels and axle boxes have to be reconditioned before substantial reassembly can be carried out. I.E. not until all four axles are servicable and back in place can the spring ringing be rebuilt allowing the locomotive to "sit" at the correct level and allow the rods and valve gear to be correctly fitted.
See the update 1/12. We think we now have this cracked.
The ferrules are pretty firmly driven into place by the expander so rolling would not make any great difference. The real issue is that the tube sheet is quite thin (a 3/8 inch sheet) so the ferrule does not have to move far to cause a major problem. The expansion must be absolutely flat (or tapered towards the firebox as the expander punch does) since any taper toward the boiler will tend to drive the ferrule out with great force that no amount of pre-expanding the ferrule with withstand.
I understand that you guys are in the process of reassembling 1630, but when it comes time to do a steam test, or even test runs, would the steam team leave the boiler insulation and jacketing off until they are positive that everything is in working order?
There will be a number of hydro tests before steam testing that would detect any leakage in most areas that will be lagged. Lagging will not be done until the areas being covered have proved pressure tight but will be started as soon as they have. So most of the lagging will be in place before steam testing.