Rear diff is 0.02 out IIRC and will not hurt the VC.....Infact putting a 2wd rear diff/beam in a 4x4 is a cheap way of getting a very strong setup. So going from 2wd to 4x4 the back end will be fine...no need to touch it.

The front chassis legs have a small half circle cutout in them to clear the shafts at full suspension compression otherwise the front chaft would hit the chassis leg...simple mod probably take about 1/2 hour with right tools/equipment.

2wd 4 pots will not fit 4x4 hubs, theyre designed for different calipers....the 4x4 caliper and disk setup provides better braking force anyhow...you might be able to make up a bracket or modify calipers to fit the 4x4 hub if you tried to...not normally a mod people do though.

I have a few 4x4 bits for sale if your interested in whats left you could save some dough as I want shot so will sort you a good price got shafts...both 4x4 cos an xr4x4 (slightly longer to suit lowered cars), 4x4 sump, x-member, props Fr & Rear....and a few other bits.

The whole front end suspension wise (bar hubs) of an xr4x4 will fit and work fine, you dont have to buy cossie stuff....think the rack might be slightly different to a cos (IIRC cossie is quick rack??? not 100% sure) but would keep costs down.

To save me typing up a huuuuuuuuuuuuuge post pm if yu want with the setup you currently have and what you want to do and I'll tell you exactly what you're going to need.

If you intend to get a bara box (speak to marco polo on here if you do he gets the best price for them), with a 2wd rear end and a decent front diff you'll be on your way to laying down some serious rubber.

Cheers
Dan