To complete this:
Lift the van up so you can get under the front, from the front.
Disconnect the battery (unsure if needed, but... AND make sure you've got the
radio code this time...!).
Disconnect the alternator cables you can see from the top. In this case, two eye connections on one terminals secured under a rubber pull-off cover, and a connector released by releasing the securing leg on the side of it, hard to see, under.
Under: remove the long transverse pipe to the intercooler.
Remove the auxiliary belt: get a 16mm socket on an extension bar, long handle or similar, and set it on the tensioning pulley of the belt. It's easy to work out which this is by looking. From above, push the long handle backwards, and you will see the pulley move back, which allows you to joggle the belt off one of the smooth pulleys and then remove it (you could probably do this from underneath, but I found it easy enough from above).
When the belt's off, remove the bolts holding the alternator on.... 2 x 16mm, plus the larger "nut" holding an idler pulley on (I used a big adjustable, did not measure side, th others are 16mm).
Remove the alternator. From underneath, lever with a screwdriver, and work the alternator body about until it comes off. Heavyish, you would not want it to land on your head.
