Just had a look to remind myself. 4 X 5mm Allen bolts on the front and 1 on the back let you take the case off. Be careful how you lie it down after this as I'm assuming you don't have the frame for the back.
You'll see there's quite a few bits to get through.
Yes, (5?) bulbs wired in series. A 'field repair' was to bridge the broken filament with a bit of fuse wire. This slightly increases the voltage to the remaining filaments and will not last as long as replacement of a new assembly, but it works, for a while anyway. It also reduces the amount of bits you need to take off.