If i can chuck a couple of ideas in;
- Check with the guy who's going to lend you a hand first what they can do and what the feel like doing, don't drive to the other side of town with a VN and an engine in the boot and ask for an engine changeover
- With possible repercussions about stuffing things up, it's unlikely some kind of ****-fight will start over this, but a way to avoid this might be to have a flat-out principle of showing whoever how to service whatever, rather than just doing it for them
- I don't know what kind of organisation will go into this and I dunno what kind of people garth has been hangin around
but having a rule of "turn up with the slab" might be better
Lastly, if you can't make it, be polite and call or sms the guy