Beware actors who protest their image too much. In the case of Franklin J. Schaffner’s “The Boys From Brazil”, the thespian in question is none other than venerable good guy Gregory Peck who makes a career backflip to the darker regions of human nature by tackling the role of nefarious Nazi Doctor Josef Mengele, a turn of dramatic ambitions that Peck seems to relish, yet is sadly inadequate to the task. Not that he’s assisted by surrounding cast of scenery munching screen Aryans including an odd turn by the usually reliable James Mason who plays his Nazi conspirator as a tourist of Key West club spots. The film follows the plot of Ira Levin’s source novel fairly closely, though Levin’s signature finales with evil seemingly emerging triumphant is obscured in no small part by a terribly staged final confrontation and the ruinous, multiplied non-presence of newcomer Jeremy Black, perhaps the worst motion picture discovery since Smell-O-Vision, though equally odoriferous. This mineral deposit impersonating an actor has been generously granted the opportunity to fail in several roles, each distinguished by a different accent, none of which resembles a legitimately recognized echo of human speech.
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CHANDLER SWAIN REVIEWS 
One of those rare occasions when I had read and enjoyed the book quite a long time before seeing the film. I was also bitterly disappointed by the awful boy chosen for that key role. That alone ruined what was in many respects a decent adaptation. I agree with you about the scene that stood out, and would also have liked the rest of the film to have lived up to that.
Best wishes, Pete.