I see some corrosion in a few areas like the CPU voltage regulator and some traces between ISA slots. There are likely some broken vias that need attention.

That's due to improper storage , for now it's only the protective coating . Anything that's mapped on the 496 work's ( all pci slots / ide connectors / ram slots / cache / it boot's into OS / runs apps / tests / no mouse thou and i don't have a pci card for that ). It's checks out with the multimeter , i've tested also the voltage regulator before putting the cpu , the fault was there before that .

bios and keyboard are wired thru 85C497, https://dosdays.co.uk/media/sis/SiS%20496-497.pdf pages 93 94 96 97 pinout
use multimeter to buz out all ISA signals to corresponding pins

That is why first i was intrigued that the keyboard works and it posts , but noticed in the diagram that they are connected trough a X bus inside . Did that and they check out . Swapped the LS245 also , same thing . Can it be a partially damaged 85C497 from a bad/shorted ISA card ?

so you confirmed all ISA signals have good connection to 85C497 or 245 buffer?
next step would be measuring resistance of all ISA signal pins
then probing signals on isa bus with a scope/logic analyser