He might have run rim brake before.
Or if he kills the disc he can just put a HS33 on there and still have a decent brake.
And yes, I can see that he has a disc-only fork.
He might just have used the wheel before he went disc though :o
It might not be a dicta.
What the f**k are you on about? That freewheel is crap. It doesn't matter if it has 21 or 42 engagement points, it's still shit.
21 EP Dicta freewheel, with tolerances so sloppy that only one of the two pawls engage at the time, giving twice the amount of engagement points, but half the strength.
Wide or thin?
For wide, go Alex DX32 / Planet X BMF / Onza Full-Fat / Echo / Megamo... They're all very similar and a pretty nice rim, Echo seems popular atm, drilled and all that.
For thin, go Mavic 521. It's thin, but strong.
Adjust the slave cylinders so that they're all the way backed out from the rim. Unscrew the TPA so the pads fully return.
Remove wheel and measure the distance between the pads. If it's >47mm, you can fit one.