For reference, I set my 8903A with the high output connected to the high input, no termination, 3V amplitude and dialed in your frequencies. My unit defaults on power-up with the 80 kHz LP filter enabled, so that's how I left it. Both front panel float switches were set to the ground position.
I got between -90 and -95 dBc at 20, 100, 250, 500, 1K, 10K and 50K frequencies. With the 100 kHz frequency, I turned off the 80 kHz LPF filter and got -76.6 dBc. With the LP filter off, the readings at the lower frequencies were all about 2 - 4 dB worse.
And while I'm thinking of it, you might want to reseat all the boards and give all the pots a jiggle (after you have marked their positions). Perhaps a pot is dirty and needs a little jostling. Also, give all the boards a good rap and see if anything on the display changes a lot. The notch filter tune and balance adjustment is particularly sensitive in my opinion. They use a single-turn pot and you had better have a very steady hand! In fact, on my unit, I actually replaced that pot with a ten-turn variety so I could really dial in the lowest distortion.