Just as slow as before mods..

I noticed that too. He has a really heavy differential in there that's Overkill, he has a overdrive transmission which eats up power but not only that..it has a numerically lower first gear 2.45? The 904/998/999 had lower 1st up to 2.71 or something right...
... And then he probably had a cam thrown in that sounded like it would be a power maker in the description...but quite possibly he has stock replace or a non blueprinted compression ratio..coupled with stock'ish timing, possibly not degree'd and taller tire offsetting the rear 3.73 .
Just what I first think of from the opening post.
Makes sense now. Everything done to the car was recommended by the classic car performance shop that had many hot rod cars in the shop and great reviews.