Hello Peter,
Many years ago I came to the conclusion the more holes you drill in a boiler the more chances you have for leakage, so these days I never fit expansion brackets, angles or what ever, Martin Evans and before him LBSC style to a boiler, now I'll always fit a couple of pieces of either suitably sized angle or pieces of square material to the frames and sit the boiler down on it's foundation ring onto the angle; it's a far easier proposition when getting the boiler level in the frames; the boiler will never jump off, it being held in place by the plethora of pipework together with the cab! It's an easy enough task on the full sized locomotive to fit brackets etc but not so simple in our sizes.
As Julian has mentioned there is the odd inspector out there who is adverse to the idea of drilling and tapping into a boiler and although it may be seen by some as not best practice I cannot recall the method being prohibited in the current publication from the Model engineering liaison group.
Regards,
Bob Youldon