Something just occurred to me. Accufab makes some very nice coolant nipples for the front of the block that can work back there also if you judiciously trim the manifold flange on the passenger side of the head. This is what they look like;
They can be had with up to a -16AN nipple which effectively duplicates the OEM front coolant crossover flows. Here is a link to the Accufab page => Cylinder Head Water Fitting
To use them at the rear of the heads, you will need to massage the edge of the intake manifold on the passenger side. At $129, I think they are a little pricey. The flip side of that coin, however, is the fact you will probably spend that much in time and parts duplicating them and not look or work as good.