I use Vectric Aspire (www.vectric.com), it's a nice CAM software that gives me good control of milling 3D shapes and would make milling the headstock a piece of cake. Your idea of angling the headstock to mill it flat will work, but I find it very difficult to do accurate work when I do things like that.
I also have a DIY CNC router made from aluminium and MDF and use a Kress FME1050. I use very fast feed rates and shallow pass depth when I work with aluminium. This keeps the tool from clogging and as long as the part isn't small I often don't even have to lubricate. With a 6 mm single flute carbide end mill I would try to run 15000-20000 rpm (2 to 3 on the speed control dial on the Kress) with a feed rate of 1700-2200 mm/minute and pass depth of 0,2 mm, maybe slightly shallower if it's 7075-T6. You can mill at a slower feed rate I guess but I would you run at 10000 rpm to reduce the heat and need to lubricate constantly. I prefer three and four flute endmills myself for aluminium and run three to four times faster than I would with single flute. Here's a little video of the machine milling some aluminium at 6000 mm/minute: "http://www.youtube.com/watch?v=OnlRMvJoycQ&feature=channel_page"]YouTube - CNC-milling a little shaft coupling
Rastering back and forth doesn't work well with aluminium because that means you're milling conventionally half of the time. Climb milling is the only way to work with aluminium.
WD40 is great, but messy. I use WD40 and then spray red spirit near the end of the job which both lubricates/cools and cleans everything up nicely. Red spirit (and maybe other spirits) also works great on aluminium but is a bit more smelly. You can see me spray red spirit on the part in the video above.