I removed C9 and C11. This allowed much better bandwidth but overshoot was present and it varied depending on the input voltage setting. So what is needed is a different overshoot trimming capacitor across each gain setting resistor. That is 6 capacitors for channel A across each of R13,R17,R21,R11,R15,R19. These could be soldered on top of the resistors when proper values are determined.
For the sake of the experiment, I made capacitors from two short lengths of thin teflon coated wire, twisted together and fitted these across the R’s. I acheived acceptable compensation on all ranges and got bandwidth up to about 10MHz with good pulse response enabling me to easily display a 100nS pulse with 20nS edges.
A note on the probe compensating capacitors is in order. For ch A. the influence of C3A and C5A interact depending on voltage setting, making setting up difficult. The method I used was to inject a 10KHz squarewave and adjust for best shape while switching between the 0.5v and 1v ranges.