Big bolt pattern and disk brake conversion

Professor Fate said
YES THEY ARE DIFFERENT! As stated, and as outlined in his link.
Different upper control arm, different spindle/knuckle, obviously different caliper and adapter and rotor, different master cylinder, different proportioning/distribution valve, different line routing... Different!
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Different caliper?I don't think you're getting what I'm asking. So I'm going after 73 to 76 a bodies for parts and find a drum brake car. Are the control arms and knuckle any use to me with trying to convert my early a body to big bolt pattern and disk.