Omega B – VFL – V6 – Questions about my winter project

Hi people, since the Omega goes into hibernation at the end of the month and I would like to have been swarmed for a long time by a few rebuilds and I will put them into action. First I dedicate myself to the rust removal and that is to say the whole cart is disassembled and examined for rust. Then it is completely repainted Question about rust: I don’t necessarily want to take out the disc how high is the probability that it rusts under the rubber? So as another project the 2.5l flies out and a 3.0 gets a new place and the question: Even if each seller assures you that the engine does not lose oil or otherwise has no quirks, I would like to know from you what should be directly renewed on a foreign engine without testing it in the built-in condition? Does the 3.0l need a different transmission or Diff? (The 3.0l is delivered completely with all attachments except transmission) And as another addition comes a threaded drive with new tires and rims on it, but to the chassis I have a question: Which parts would you renew during the chassis replacement? Trackbars ? Crossbars etc.