I ended up keeping the ALAN Alu Cross after all. I decided to stick to my initial plan to make this a budget build and so I sold off all the other bikes and parts I purchased for this project. All but the groupset that came off the Diamant cross bike. You can see the end result below.
I did my first 50 km off road ride last weekend and everything worked like a charm. Some quick notes:
Headset: with the EDCO headset fork shudder has virtually disappeared.
Brakes: the Shimano LX cantilever brakes were very easy to set up and provide superb power and modulation, even though they are mated to drop bar levers.
Bars: the On One Midge bars are great for single trails, but did take a bit of getting used to.
Single front chainring: the chain has yet to drop and supplies smooth and silent running even in bad conditions.
Saddle: bad idea to put a leather Selle Italia Turbo on a cross bike! The combination of sand, water and constant rubbing has turned the smooth black surface into a suede like one.
Tires: the Schwalbe Smart Sam Cross tire is a good choice if you do both off and on road riding. It isn't as fast as a road tire on the road or as grippy as full on cx tire off road, but does combine both disciplines really well.