Well, just to let you know, I did it successfully
I now have a Dyson I can use all over the house.
There's a great exploded diagram of the two types of head assembly over at espares
, hope they don't mind if I link to it
. The parts I ordered were:
Cleaner head assembly (1)
Brush housing assembly (6)
Clutch actuator outer (7)
Clutch Assembly (8 )
Clutch Cover (10)
Brushroll Assembly (12)
Soleplate Assembly (13)
I managed to get a combination of new and second hand parts, total cost was under £40.
Using the information at Dyson-online's technical advice pages
it was pretty straightforward to work out how to disassemble the old head and reassemble the new one.
I'm still not convinced that a DC04 head wouldn't fit on a DC07 - I'm certain that many of the parts I received were actually DC04 parts, and they all fitted together fine. I'm loath to recommend anyone to go out an buy a DC04 head in case I'm wrong, but given that I could have bought a complete DC04 head for £10 or so (!) I do wish I'd given it a go myself - if it didn't fit I could have just ordered a couple of new DC07 parts rather than the whole lot, and the total would still have been less than I paid in the end.
Can't complain though - in all, it was a lot cheaper than a new vacuum cleaner!