Boy that is one congested piece of test gear.
From what I gather, it sounds like the output level was factory programed to a flat response at the various RF/IF frequencies for each individual VA-62. So any variation at lower IF frequencies is likely coincidental and would need to be programed out via Eprom.
Are you guys pursuing these units to use as an IF marker generator; to be used along with another sweep generator? Or are you planning to use the Sencore multiburst modulation method of IF alignment?
I'm curious just how well the Sencore multiburst alignment method caught on with repair techs? For my hobby use I think I'll prefer to stick with the old tried and true scope method of actually seeing the IF response curve on a scope. I can however see the practicality of the burst method for a busy repair shop.