With 230,000 miles on the engine and being run with little anti-freeze, that engine is likely to have a good amount of rust trapped in the block around the cylinders. The used engine I swapped into my truck had about 100,000 miles on it and had a good bit of rust around the cylinders. If you are pressed for time, go ahead and flush the block by removing the block drain plugs, however, with 230,000 miles on that engine, the freeze plugs are likely to be fairly rusted (on the back sides of the plugs where water has run across them) and good candidates for replacement anyway.