Tom, that's actually the plan A if there is a problem with condensation in the crankcase!

Thanks DMIOM!!

Today's tasks:
I completed drilling the head bolt holes, and they all line up. I must ]have removed all of the old pilot drill bit, because that hole drilled fine -- I did leave it until last, though.
Then I thought about drilling the valve bore. This is a tricky one since it is 6" long and should finish out to 1/2" in diameter. It goes straight through the casting from one boss to the other.
Having just recommended to someone else on the forum that they drill a long hole by coming in from both sides, before boring to final ID, I figured I'd better take my own medicine and do it that way, too.
My 1/4" drill bit was barely 3" long, and I planned to start with that. Since I'm also doing a thread about my Gingery lathe and the use of faceplate and angle plates to do a lot of work, I decided to do the same thing here to drill the hole. I have a Sears/Atlas 12"x36" lathe now that is somewhat accessible in an unheated storage shed. The Gingery lathe is packed away.
I used some of my Gingery lathe angle plates to set up the drilling operation on the Atlas, just as I would have in the past. The head casting was bolted to one angle plate, and a reference line squared to that. Then the angle plate was bolted to the faceplate (off the lathe and in my much warmer home). Then a short trip to the brisk machine shop atmosphere of the shed carrying the faceplate setup. Metal sure gets cold fast!
Once the faceplate was mounted, I brought the tailstock up to the casting with the dead center in place, loosened the angle plate/faceplate bolt slightly and tapped with a soft hammer until the casting drill mark was just touching the point of the dead center. I already knew the casting valve center line was square to the faceplate. I just tightened the angle plate bolt, and was good to go.
I had also mounted a second angle plate to the face plate as a balance weight. I engaged the back gears and set the belts to a speed of about 60 rpm. I first checked that I had clearance all around by swinging the lathe by hand before switching on, and also did a last check of the squareness of the valve centerline with the faceplate. To start the hole I faced the boss, center drilled it, then mounted the 1/4" drill bit for the first hole. Everything went well, and I made sure to clear the drill frequently.
After I drilled right up to the end of the flutes on the 1/4" drill, I switched to a 3/8" drill to open it out more. This went quickly.
Then I unbolted the casting, turned it around, remounted it as before, and drilled from the other side.
