I know, 25 is the magic size.. um.. Star Wars? that's somewhat popular..
But I suppose an arcade monitor is the better start for such a thing. Eliminates a whole lot of circuits not needed..
anyhoo,

Mr Jrok

is the man.
he built one out of.. a Happ kj-1915,
ampliphone deflection board and a hand-wound yoke..
(yep, same guy who makes the Williams multi board using the original processor type)
So.. it is remotely possible.. convergence seems to be an issue, though.
Looks like this page is from October 2006..
Maybe one of us could get brave enough to ask him how it's progressing on the vector things..