These things are problematic at best - I have not had
a good experience with any current offerings. For what it's
worth, my two, cents is that they will eventually stick, and
probably in the closed or partially closed position.
I removed them from both my '66 Chevelke and '69 Camaro
and replaced them with the donut replacements.
Unless you absolutely have to have it original, to me
the problems far outweigh the benefits. Both of my
cars start easily - and I give them a few extra seconds (10-15) at
idle when I first start them, but other than that you would not
know the heat riser valves weren't installed unless you physically
went and looked.