Just had a look at my old TMAC loading manual (yes, I'm one of those sad people that has a full attic!)
Heres some figures for comparison
MTOWT 210,000
MLWT 165,000
MZFW 160,000
Guppy basic weight 98,500
APS Fr/Lr config. 102,000
Therefore maxload 58,000
So with 3x 10,000lb RB 211 engines on board it could land with about 15 tons of fuel. The cargo bay is 84' long (with another 14' in the swingtail) . It would have been able to manage 5 engines and land with about the same amount of fuel as the L100.
Politics and the loss of the aircraft in Anchorage put a stop on the second Guppy being built.