Cossie hubs are different to std 2wd hubs, which is what xr4i uses, suspension rates all different, cossie prop different, and importantly has CJ13 flange at diff, styd one would break with cossie power, xr4i uses 260mm discs single piston sliding caliper 2wd cossie uses 283mm 4 pot calipers with rear discs(273 solid).
All the 4i stuff could be used as upgrades went along though allowing you time to find the needed bits.
Cossie has lsd, 4i doesn't, defo needed as well, as is rear discs.
tabetha