PCB design for 2 Arduinos nanos with 2 Mcp2515 and connection between them by Tx Rx

I need the PCB 2 Arduinos nanos with 2 Mcp2515 and connection between them by Tx Rx
I need also to connect all analog pins from one Arduino and digital pins from another Arduino to 24 plug

ECU plug: HCCMHPE24BKA90F 24 PIN 24 WAY ECU CONNECTOR
PCB size: 76mm by 96mm and the plug in the 76mm

I need it to fit in the this case:
https://www.aliexpress.com/item/33009248388.html?spm=a2g0o.productlist.0.0.32f952ceHWptXt&algo_pvid=5de5b527-55e0-447a-93f0-e73f1946be5c&algo_exp_id=5de5b527-55e0-447a-93f0-e73f1946be5c-7&pdp_ext_f=%7B%22sku_id%22%3A%2210000000650170031%22%7D&pdp_npi=2%40dis%21SAR%2129.5%2124.8%21%21%2125.38%21%21%402100bdde16646976721808203e0bf7%2110000000650170031%21sea&curPageLogUid=7MXMrSUjLTHq