Huh?
Boeing sold the 767 as having "The widest economy seat ans aisle combination of any widebody airplane available today".
Although, of course the A310 has a wider body with the same 222 in fuselage cross-section as the A330.
Now, the non-ER 767s have wing tanks only (50.5 tonnes) and the -ERs also have centre tanks of 11.9 - 22.5 tonnes. The KC-767A was supposed to have a further 18.6 tonnes in additional centre tanks, for a total of around 91.6 tonnes. But the additional center tanks feed into the center tank - so without that you're pretty well stuffed trying to turn old 767 non-ERs into acceptable AAR aircraft.
Unlike firebombers, AAR aircraft do NOT have specific 'AAR tanks' - the whole fuel system is used for both receiver and tanker requirements.