Its possible to have a precise propagation delay compensation in 2465B. I recall it is in one of the test or options accessed in the CAL menu.
For the test of channel match, use a single 50 ohm ext term at the BNC T and leave both ch on 1 meg.
The P6137 is the ONLY 10X that is specified for 2465B, at full BW and is capable of 400 MHz in 2467.
For fastest probing use the Zo probes P6156, 50 Ohm scope input and 500, 1000 ohm load BW to GHz. (not cheap, had to get the full kit)
To learn the technique and theory of probes, I Highly recommend the TEK Circuit Concepts book on Oscilloscope Probes, BAMA or TekWiki should have the PDF.
Just the ramblings of an old retired EE!
Happy 2021!
Jon
Jean-Paul