A - Where possible, the original poster's wishes is to be respected. Where their wishes aren't clear(e.g. the creator didn't forbid mirroring), it can be possible to post their material, as long as the creator is clearly cited. If they complain, it would be taken down, if they register, it should be turned over to the proper owner(once Forum Staff is informed).
B & C - Preferably port as-is, however, each forum software uses different tables, so editing of layout elements is generally fine. It should be also clearly marked somewhere that you edited for readability. If actual content is altered, you should probably make it "Based off <foo>'s work on <original material>", and post that way.