Hello Philip,
Don Young's 'Newport' 7.25"g design has an A1X smokebox. Reeves could supply you with the relevant drawings.
Alternatively, all you need is a piece of tube 4.312" OD, 2.910" long. My front and rear rings are from stuff I had in stock, and I rolled the tube and silver soldered it.
The 'drumhead' smokebox sits on a saddle with an elegant profile. There is no casting available for this, so I fabricated one.
The smokebox door is 3.218" diameter.
Note that Martin Evans drew the A1 smokebox and door too small in diameter.
The following is from one of my albums on here.
Cheers,
Julian
