Sounds like the new yoke is not specced right for your monitor chassis.
I think Toshiba, NEC and Panasonic TV tubes can be used as replacements for Nanao tubes. You might be able to find one in the dump, or get a cheap old 2nd hand TV. So, just change the complete tube (and yoke, together) and attach it to your old Nanao ms8-29s chassis. They are a good quality arcade monitor.
If you have the original yoke's vertical and horz impedance values (measure resistance of the yoke coils with an ohmmeter, or maybe someone on this forum can help), then you can confirm the replacement tube/yoke compatibility by comparing these values between the old and the new. From memory, Nanao 29" yokes have quite low resistance, especially on the horz yoke coil.
I have a Nanao MS8-29 here, so I can measure these yoke impedance values for you if noone else has them handy. I'd just have to get into the back of one of my arcade cabs first.