think I've found a proper match, only
to discover that the replacement CRT has a different deflection

It's not only that. Nowadays you need to match the yoke to the internal
convergence poles. In many cases you find that even if the deflection is OK,
you can't get edge convergence. It's off in a way that does not respond to yoke
tilt properly. Many times you might get close on everything but the H lines at
the top and bottom for example.

The only way to see for sure is to plug the chassis into the CRT and look, and
I always do this before actually installing it if the numbers don't match.

The specs that'll tell you this are likely to be complex, such as delta field @
max V deflection @ vector XXX degrees or something like that.

Simple deflection angle is actually moulded into the CRT bell, or used to be,
it would be like 27V90, 27V100 etc., not to mention there are different degrees
of arc across the face. Electrically these tubes could all be the same, maybe
even use the exact same gun assembly, it's the variables having to do with
magnetic fields that trip you up.

JURB