What type of difficulty can I expect in attempting to replace the full
carpet in a 1986 'Vette with a Carpet Kit ordered pre-cut from one of
the manufacturers out there?

Removing the adhesive from the original carpet? Replacing the molding
and body parts over the carpet? Are the rear deck storage lid just
covered with the carpet or will there be anything to remove from them?
Is there any other prep that will have to be done to the car surface
once the old carpet and any residue is removed like using some Goo-Gone
or ....?
What about the stock carpet color, is there any place besides the
invoice or any build sheet that it is noted on the car in case being
original could be a concern later? Any estimates on time?

not much. i did my 89. r&r on all the trim and seats took the most time.

regards,
charlie
cave creek, az