Check the manifold to head joint, it distorted one relatively new bikes (still under warranty)
Check vacuum ports on head, pretty sure you have the rubber boots which crack or just fall off if you don't have the correct spring clips on them. Do your carbs have the separate o-ring at front right next to diaphragm seat? (I forget which models had them), they are often missing and cause an air leak. Check the plastic carb tops are not distorted from overheating. Check float level and set it to minimum height (there should be a stainless steel 'adjuster plate' on the plastic floats) Oh, fit a better regulator and rectifier, Suzuki are well known for fitting cheapest ones they can fins and are not very reliable (and they still do the same 40+ years later)
Check and see if the GS Resource is still up and running, I haven't visited it in probably 10 years
Just updating to close this out... after replacing the head and base gaskets, rechecking valve clearances, replacing/adjusting the air mixture screw, readjusting timing and adjusting float levels, the bike runs great. I think it was a combination of small problems all contributing to the issue. I still need to sync the carbs to smooth out the idle a bit (not bad now) and then I think I can just ride and enjoy.
Thank you all who contributed suggestions!