The 6EA8 mixer - pin 2 grid test point is at L8, see lower right diagram, left hand bubble 1 and 6 point to it on one of the switch wafers.
The 3.1 MB source JPG was reduced by this site to 106kB so it may be fuzzy but shows the location.
Appears to NOT be a feed thru, so it needs the cover off to access it. Hope you are successful.
KRK98 tuner new vista.jpg