hiya, did the kingpins in mine a few months ago, takes about 20 minutes a side tops.
It is a bearing, the part you knock out is the outer, so you'll get that when you buy the bearings, i picked it up from a company in bristol, cost me about £60 for the 4 bearings. I didnt replace the rubber seals, just gave them a good clean and put them back in carefully, but i guess if yours are in a state then worth replacing them. I've got very flexible brake hoses so I just hung the callipers from the bumper while I was doing it rather than removing callipers totally and bleeding brakes after.
Any other q's let me know, drop me a PM as I dont check this much.
Cheers
Henry