The Cyclone and the Pro 4 share their hubs and wishbones, amongst other parts. I agree that the standard knuckles and possibly C-hubs aren't too strong but you can always get some aluminium ones which will sort your problem out forever.
The rear diff will fit in the front.
It depends what sort of things you are likely to buy for your standard Cyclone as to whether it's worth it or not. There are a few interesting parts in there which may be worthwhile, such as the updated bulkheads, thicker driveshafts. Also, if you are wanting a spool then the Hara/Surikarn ed is probably worth the extra money as you will then not have to buy a spool and solid pulley separately. The next question is are you bothered about the bling and speciality factor? The Hara/Surikarn eds look extrememly nice and from what I gather they are quite limited as to how many there will be.