What is your question? Are you asking about swapping interior items from a MkIV to a MkIV? Across trim lines? Across years? Across models? Across makes? It's a little unclear.
Your primary source for interior parts, if not another wagon, will be a MkIV Jetta sedan or Golf. Some years will have different wiring. Front seat forward will be mostly the same. Wagon rear bench is different, but can be modified. Rear door cards are shaped differently between J and G, but can be disassembled into pieces if needed. The trunk of the wagon is mostly unique.
There are lots of threads on interior swaps, a search will reveal lots of great info.