Note the holes go all the way through the barrel and the reinforcement plate. Also note the two cut outs at the smokebox end to miss two rivets which hold the chimney saddle to smoke box. These are needed as the end of the boiler falls half way across the holes.
Drilling for the water pump. Again these are throgh holes and Phosper Bronze bolts will be made to bolt all components to the boiler and a suitable loctite will be used to seal, along with a gaskets.
The aluminium jig was bolted to the milling table to support the boiler so it could be rotated to aid the positioning of the drilled and tapped holes around the circumferance of the barrel.