Jumper 3C3 is only found on very early II series boards. On the newer boards (which the majority of the series had), 3C3 is replaced by 3C8 thru 3C11, which are found next to the tone filters.
To enable Set 8 (A-B, C-B) paging on the majority of II's:
3C1 - OUT
3C2 - OUT
3C4 - IN
3C5 - OUT
3C8 - OUT
3C9 - IN
3C10 - IN
3C11 - OUT
Note that with Set 8, you'll have to actually cut the traces on 3C8 and 3C11 with a sharp X-Acto knife or razor blade to break continuity, they are not solder pads like the rest of the jumpers. 3C9 and 3C10 are regular solder pad jumpers, which you would close after cutting the traces.