For library, is this one of the applications on BB board that is the gateway between J1708 and serial port?
GitHub - freddy120/UARTJ1708_atmel: UART for J1708 on Atmel AVR ?
Potentially you could do J1708, not sure if there is anything that already exists.
If the timings are not to strict you could probably do it from user space and just use the UART with appropriate interface chip. This would certainly be the easiest option, especially if you are only listening to the bus.
If you can’t meet the timings then you could potentially use the PRU’s to do J1708, but that would obviously be a lot more work and you might find it easier to add an additional MCU to handle it. It would probably be easier than trying to debug the PRU code.