UPDATE:
success!
the modification I have mentioned before works! the issue I was running into was my varification. since a square wave has a crest factor of 1 the rms output should match the average value before any sine rms correcting factors I think. so before modifying the voltage divider in the rms to dc converter circuit I couldn't see a difference before or after the modification so I assumed I wasn't doing anything. NOPE I was just being dumb.
I only had a square wave calibration signal from my osciliscope as a referance. so to varify the conversion I went out to my cegep to test and do a rough calibration with their function generators and multimeters.
I had replaced the 4.7 uf electrolytic averaging cap (C115) with 2 orange drop 1uf polyproplene capacitors (for worries about leakage currents) and the 100k (R115) resistor with a 120k resistor to make an equivialant voltage divider to the 100k 64k one in the 175.
I wouldn't worry about modifying the c133, r139, or c132 I mentioned in my previous post.
after a rough calibration where I compared a signal generators output with three aglient 34450a multimeters and adjusted my keithely. I was able to get ac voltage values within a 0.5-4% error of the other multimeters readings across various waveforms.
I'm fairly happy about this mod
I hope any other keithley 175-av owners can take something from this.