Well I'm getting ahead of myself here again. If I were to build up an engine from the bottom up then yes, full acid bath and flux the block looking for small cracks. A good machine shop can do this and paint it for you for under $150.
If your building the motor yourself and skipping this process, then clean it as best you can. Make sure and get at all the nooks and crannys and use a pressure washer if you can.
But a good word of advice here, parts are expensive. If your putting in performance parts they're really expensive. Dont risk a major build up saving a few dollars by skipping the flux and acid wash. If theres even a minor crack, the heads or block are never going to last.
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