No need to get a used IP from the exact same truck. The differences between models are minimal and any IDI IP will work. If your looking for a core for a rebuild, used is fine. If you are looking for an IP to use on your trunk now, used is huge crap shoot and the metering valve will almost certainly stick and cause the truck to die on decel. That may be termporary or permanent. I'd suggest a rebuild rather than a used IP for the truck.
Heath