Barnes Commentary (which can be downloaded with eSword) :-
The idea, however, would be conveyed by this language that he did this personally, or by himself, and not merely by employing the agency of another. It would then be implied here, that though the instrumentality of Noah was employed, yet that it was done not by the Holy Spirit, but by him who afterward became incarnate. On the supposition, therefore, that this whole passage refers to his preaching to the antediluvians in the time of Noah, and not to the “spirits” after they were confined in prison, this is language which the apostle would have properly and probably used. If that supposition meets the full force of the language, then no argument can be based on it in proof that he went to preach to them after their death, and while his body was lying in the grave.
If I've understood it correctly, the concept presented by Barnes would render the verses something like :-
[color=0000CC]1Pe 3:18-20 For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit: By which[/color][color=CC0000] he had, prior to the flood, gone [/color][color=0000CC]and preached unto [/color][color=CC0000]those whose spirits are now[/color][color=0000CC] in prison; Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein, few, that is, eight souls were saved by water. [/color]
PassingThru