[Electronic M]

In any RCA based color set it should SOP to measure HO tube cathode current(IIRC there should be a .47uF cap in parallel with the current meeter) and adjust the linearity coil for minimum cathode current. I prefer to follow the Sam's horizontal adjustment procedure, for a any given set, which usually has you adjust the horizontal oscillator for optimum performance prior to minimizing cathode current in the HO tube. It should be set to 180mA(IIRC) or lower if possible. Some roundys had a 250mA (ie. 1/4A) fuse in series with the cathode of the HO tube. IMHO it would not be a bad idea to add such a fuse mounted above the chassis...It would protect the fly from an horiz osc. failure, and allow for easy points to connect the meeter to for measuring the current.
RCA based HV systems have a tendency to blow out their flybacks from running too much current through the HO tube...Which is why replacements for RCA roundy flybacks are especially scarce compared to other flys.

You have a good flyback, Please don't waste it.