It's a bit late to report, but last sunday, the overhauled cylinder head as created by Joost went back on the white Cooper. In the end, valve seats went in for all four inlet valves, because the other valves were not properly cut either (was just not as apparent as with the one valve). Joost also performed some magic on the flowing of the head, and reckons the head should already make a good difference.
Now armed with some measurement equipment, he could determine that the distance between the top of the pistons and the deck (top of block) is 1.3 mm, which is slightly better than the 1.5 it was previously thought to be. Combined with the 22 cc chambers in the head this should give a CR of 9.16. Still low (should be 10.3) but not as low as thought at first.
After everything went in, there was just a little time left for a quick test drive, and I didn't want to take the car for too long a drive because it was still cold and there'd be salt on the roads. The car was running OK, but I didn't get a chance to really get it warm enough to feel any difference. At least the revs were picking up well, which was a good sign.
Next sunday, hopefully the wheather is good, so we can take the car for the "Hoekse Waard Rit", to give her a proper spin.