Re Probes, cable legnth....
The P600x had relatively thick cables, and massive screw on probe tips, hats.
Meant for tube sockets and B+ voltages.
Compensation was by rotating the probe body.
The later probe's starting with 454 scopes were much smaller, thinner cables slip on hats and had comp box adjust.
Finally the extra long cables traded off bandwidth for legnth, so always look for the standard legnths.
Remember to check probe compensation for each probe- scope- plugins combo.
Jon
Jean-Paul