GC is far too honest to try to gain sales from condemning people's stuff but he is a perfectionist, conversely many 'mechanics' are happy to use any old junk if it looks vaguely OK. The corrosion on those cams doesn't look too good to me but I'm no expert on these things.
Don't get me wrong I don't think Guy would lie to generate business, it's just I know his standards and (like you said) that he's a perfectionist. In my opinion that means his attitude to risk is very conservative. That is probably a good thing in a race engine builder who's reputation depends on the quality / reliability of his work but it might be OTT for a road car where the owner is happy to take a calculated risk.
Put it another way while there may be an ideal way to build an engine there are other approaches that don't necessarily automatically lead to disaster.
You are right that he would probably err on the side of caution but it is a difficult situation with fiat twin cams these days, gone is the plentiful supply of healthy motors from rusted out cars so it is no longer wise to chance building from components that might cause failures and damage to other components but conversely the lack of new parts also means careful conservation of parts that would previously have been renewed is also the option.
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