Some of the headset pieces can be put in upside down or in the wrong order. When I do this I am extremely careful to lay out all parts in an order and correct side up so I do not muck it up. If I start the project and can't complete it, I put the parts all together again on the frame and use string or twine to keep all parts on the frame in correct order and orientation. If you have no string, tape or zip ties could suffice.
Setting the race on the fork might take tools you do not have. When removing the old one from the fork, take care to not damage it. When I recently bought a suspension fork for my Nomad, I bought a spare race so that I did not have to move race from fork to fork and back and forth.
If your old fork was cut and the steerer tube of the new one is uncut, you might lack spacers. You can reassemble and ride it but it is very hard to get the headset bearings properly set, but you could ride the bike to a bike shop.
Do you have a spare star nut and tools to install? Bike could be ridable without it, but you would have to ride to a bike shop first thing.
Not sure about the headset you have, when I do this with a Cane Creek headset, I disassemble the bearing parts and regrease - but you being on tour, that might not be a good time to do that without any solvents or containers to store the ball bearings in, etc. I just mention it as a side note.
I did a google search for a diagram of the Orbit, found this page from this forum. May be other good info here. Especially the diagram, item 8 is the fork race.
http://www.thorncycles.co.uk/forums/index.php?topic=2636.0Good luck.
