Champions Pack includes...
- Shocks (which are the same size as the BX Worlds - if you have an older BX you need to source the longer shock shafts)
- Rear anti-roll bar
- Titanium turnbuckle set (don't know if the BX ones will all fit).
- Front wheel hexes
- Adjustable kingpins
- 81T spur
Of the list above, the most useful things will be the shocks, the anti-roll bar and the front hexes. You are pretty unlikely to need the 81 spur (BX one is different), the kingpins offer an adjustment that I don't think anyone uses, and the kit steel turnbuckles look quite strong anyway.
Of course - all this is hypothetical as neither the cars nor half the parts for them are available in the UK right now...