Just an insight on core support cutting to make removeable. Cut the core support as wide as you can the first time. A narrow opening is all most as good as no opening.
Are thes mounts designed for the 240SX KA or SR? Or will they work with a truck KA as well?
The truck and 240sx KA's have the same block pattern.
The SR20 is a different animal all together, not sure if was ever used in a truck.