Christopher Tumber tweaked the code a lot. Now it’s running at 48 fps (instead of the 25 before). Now it’s playable on a real Vectrex (I didn’t had one when I wrote it). The source with all the improvements is included.
And there is a thread at the Vector Gaming Forum about it: here.
Vectrex-p1x3l-pushr-improved (19.3 KiB, 8. September 2014)