No, I'm not angling to close it. I think I'd have gone for a simple multivibrator driving a pair of power MOSFETs with a bit of care to protect the gates if run at 28v. It would mean no moving parts other than the solenoids.
I was just making the point that there is an awful lot of ways of doing this and almost any of them can be made to work. It's the sort of thing that can get me mired in indecision. Sometimes tossing a load of coins is the right answer
David