Not so bad

Carefully calculated, measured and scribed lines on the outside of the valve block to enable it to be tilted to the correct angle for making the steam passages. One the scribed line was as vertical as I could get it everything was centred up and a 4mm flat milled on the inside edge of the bore followed by a centre drill then a 2mm drill. I had to run the reamer through the valve bore again to get rid of the burrs from drilling.

Measuring the position of point where the holes break through into the valve chamber isn't easy but using the 'wrong end' of my vernier calipers the hole positions seem about right (i.e. 5mm in from each end). A matching flat was milled on the inside lip of the cylinder heads to allow a good flow.

Just realised that I can now unclench my teeth - the fear of wrecking the hours of work that went into the cylinder have passed. Phew!!

Here's the inboard head showing the steam passage - I tried a shot of the other end but it was too dark in there!