I agree with the adage, "if it isn't broken, don't fix it". For sure things are complicated enough with the swap over to change an approach now.
Personally I feel "uncomfortable" with using any kind of a "plastic". I don't want to be the "guinea pig". I do understand the need for the flexibility in such a tight space though.
I have found on several occasions on my current Fords and Audi's those factory applied flexible plastic vacuum lines split and leaking for no other reason that they have aged.
That concerns me in that I want bullet proof materials as much as possible on that car. Those broken plastic vacuum lines must have been the best materials available at the time for a major manufacturer to use to begin with. Hopefully there are better materials then those available now?
Fixing something like that "on the road" is likely as close to impossible as there might exist on a Pantera? That is "flatbed time".
I have seen several applications where Inglese just used regular old fashioned rubber vacuum hose for that plumbing. I don't know if that is still the situation since all of his builds are completely custom anyway.
Why don't you inquire with him on what to use for the vacuum plumbing?