Let's take a look at this three panel sequence from FF #152. By the way, these are Jim Mooney finishes over Buckler layouts in #152. Marvel thanked Mooney for stepping in and saving "us at the last minute."
During this time Marvel was producing a large number of comics; and Buckler, Sinnott, Sal Buscema and others were working on multiple assignments including 1974's Giant-Size issues! With such a large output, looming deadlines, etc., it's not surprising there were some rush jobs and last minute "rescues"  along the way. 
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| Top of page 10,  Fantastic Four #152 | 
Panel one is a combo of two panels from FF #43. 
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| Fantastic Four #152 (1974) Buckler | 
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| Fantastic Four #43 (1965) Jack Kirby/inker Vince Colletta | 
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| Fantastic Four #43 (1965) 
Kirby/inker Colletta | 
                                             
Panel two is modeled after this one from #43.
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| Fantastic Four #152 | 
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| Fantastic Four #43 | 
And panel three is based on a panel from--yep, you guessed it-- FF  #43.
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| Fantastic Four #152 | 
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| Fantastic Four #43 |