Trying to Fit the Blowdown Valve

Trying to refit the blowdown valve onto the boiler of steam locomotive NCB Ayrshire Area No 10 following an overhaul of the boiler. Part of the overhaul involved the fitting of new studs to attach the blowdown valve onto, and unfortunately the blowdown valve wouldn't fit on! As a result some machining of the bolt holes on the valve will be required.
Doon Valley Railway
Waterside, Ayrshire