So you're changing ships and going to the PIC from the AVR that you're currently using? The above drawing is just the arduino board plus the simplified 1x/4x VPW level shifter circuit. As I said above, if you don't need the Arduino you just use the top part that includes the voltage regulation to the VPW 8V bus, and the 5V logic bus to power whatever microprocessor you want to use.
Also, not sure if you meant to link a different transceiver or if you thought there was one built into the PIC, but the part you linked is pretty much going to need all the same stuff in the above drawing, plus another interface to get from RS-232 to USB. The drawing above includes the USB interface, the complete microprocessor and all it's support components (which are substantially the same as what you need for the PIC) the power supply, and the VPW transceiver. No dongles/adaptors needed.
You could use the ATmega328p in DIP form factor too...and then continue using your arduino code instead of having to do a complete rewrite for the PIC. Still gonna need a USB interface, crystal and load capacitors, reset button, both voltage regulators, and the VPW interface, so I don't see how your link above helps you simplify anything.
Ok, so block mode needs to support 4096bit blocks, I can make sure that happens.
I thought you were using the flash tool and ADX/XDF that Dimented24x7 wrote to work out of. His software and ADX files, IIRC, are written for the AVT-852 cable, and speak a totally different language to the ELM chips.
So, what hardware is your open source tool actually using?