Also currently designing a new case based around the 42s as a replacement shell for the 30b. I absolutely can't stand the case of the 30b. It feels incredibly cheap and like I'm going to break it. Haha
As for the usb board, this here fits down at the very bottom with some slight trimming of the inside:
Ultra Compact USB to UART TTL Converter with Micro USB B Type Connector (FTDI FT231 3.3V / 5V Tolerant) https://www.amazon.com/dp/B082NKCXCN/ref=cm_sw_r_apan_glt_fabc_0R9QPH9MFZ40389M2YQP?_encoding=UTF8&psc=1
35S in Canada is about $85 in beaver bucks. Any ideas how to aquire it cheaper?