With several application specific heads in my plans this topic got me worked up and I called my FLAPS to insure availability. I was told they are no problem to get and although they have no other application than 1950-1952 powerglide engines I was assured that there are still many of those out there worldwide. TRW number is V-1998. and my price is $17.96. Interestingly I was told that if for any reason they were not available he could fix me up with $12.00 stainless blanks that I can cut to any desired length and machine the groove and seat or he has a guy equipped to do it on short notice. Easy availability of custom valves adds an interesting possibility when correcting valve train geometry.
