The old 1978 Zenith is chassis - 23KC45. (vert deflection)

The newer Zenith is model - SY2551S (missing red)

My main problem is in testing though. Most of the techniques I've read
about are for out of circuit tests I think. I have the Photofact for
the sets, and I've tried taking voltage measurements and comparing
them, but I'm still unsure hw to go about things.