You need to get on
http://www.ratsun.net/ and check out the truck forum and the Project Datto thread. I know that there are two guys on there that are building 620's from Australia. I've been on ratsun.net for about 5 months now, and have only scratched the surface for how info there is on that site. You can keep the king pins if you want. The biggest question is if you want disk brakes or not. Beebani (on here and on ratsun.net) sales a bracket that will allow you to use parts off a D21 and an Isuzu trooper, and they say that you need a bigger brake booster (sucks since there is so little realestate under the hood as it is). 620's came with disk brakes in '78 and '79 along with ball joints. It IS NOT a direct swap to the King Pin trucks though, it takes a little fabriaction to get them on. Good luck with the build!