Yes, it is possible if he has the right tube and yoke, this would be hard to find, but perhaps he has used tube and a yoke/ The yoke needs to have a horizontal impedance of about 0.24mh, vertical can be 6 to 20 mh.
He will then need to modify sweep caps for the horizontal and likely a dropping resistor for the vertical.
It is still a risky undertaking that I would suggest that would require at least a weeks of burn in with temperature probes in the vertical circuit, horizontal and B+.
At least that is the only way I would put my name on it. On a one off basis not economical and risky. If he has done it before with success, again hat's off, great job!