Pretty simple fix, I would weld a AN bung to the block like this
http://www.summitracing.com/parts/ci...0006/overview/
And plug it with this
http://www.summitracing.com/parts/ea...6erl/overview/
-16 may be too large but this gives you an idea of what can be done and still leaves the ability to drain the coolant out of the block.