Do you need an OBDII interface cable that doesn't use the ELM327 chip? I have one that's gathering dust that I specifically bought in hopes of being able to help with development for the 1996~1997 LT1/LT4 PCM interface. I think it would be far better in your hands than mine. Here's what it is for reference: https://obdxpro.com/product/obdx-pro-vt

Though mine is USB-only, no bluetooth. Same thing, though.