23,855 USG is the figure quoted for max. fuel in the Boeing figures for the 707 320 series. At 6.667lbs / USG that comes out at 159,041 lbs.
El Al's 707-420s TLV-IDL
Were they operating RR Conways? Again, the Boeing figures suggest a max. range (with normal passenger load) for the RR 420 of under 4000NM!
SD