If the crank journals are clean and undamaged, changing the shells should be o.k.
Problem arises with the rear main bearing cap removal though because it carries the rear crank seal. It would be fairly safe to assume though that if the other mains are good, that should be the same.
Got nothing to loose though by dropping the sump, removing the big end caps together with the mains caps (One at a time, to prevent crank hanging) and seeing what state they are in. If they are fecked..at least you will know for certain !!!
