Sheesh, this seems to be getting nastier each time :-(

Assuming the 6264 is new and/or proven on other machine(s) ????

You may wanna check/replace the bypass capacitor associated with the 6264 and any other bypass caps (especially tantalum types) around other memory chips.
'ghosty data' is usually corrupted ram data when bypass caps go open (or short) and alter the digital 5v signals to 2.5volts into the 'no go zone....

fingers crossed...