Agreed the sump plate is not a big deal, given the availability of aftermarket sump plates like Mainley and AutoSport to name a few.

With respect to the cases for a basis of your engine, don't you also need to consider cranks? The 3.0L 70.4 mm crank is very plentiful and relatively cheap. The later 3.2L 74.4 crank is typically a bit harder to come by and thus more expensive.