Contrast. Your Kodachrome clones lack the K-64 contrast. Try some images shot in late day sun, and recreate that heavy saturation in yellow and red. The shadows should be more “blocked in.” This is a valid concept, hope you get some positive results.
Think that’s the key! It’s trying to replicate slide films latitude. Maybe shooting with Fujis jpegs might be better as a base file at a low ISO so you don’t have the dynamic range of raw file.
I wish I still had my Kodachrome prints that I had hand printed on Cibachrome at home in the early 80s. Colours to die for and that deep bronze/gold sheen on the prints. No AI could even imagine that, neve rmind reproduce it.