Uh no. The engineer specifically notes a 707 - not a 747.

707: 57000 to 67000 kg weight; 17,400 gallons

767: 80,300 kg; 24,400 gallons

1/3 greater weight AND fuel load.

Furthermore, there are all manner of other assumptions such as assuming that the steel rods were to spec; that there was no degradation; that internal fire suppression and other safety systems worked correctly etc etc.

Conspiracy theory operates primarily via the impossibility of disproving a negative - and seek to fill in the null hypothesis with any and all theories.

Yes, Not all conspiracy theories are nonsense but the vast majority are - and this one is.