I'm seconding John Sargent's method, and would avoid using power tools. I use an old woodworking chisel that I resharpen on the bench grinder as my scraper, and plug ALL the holes in the block deck with bits of rag or paper towel. I also put oily - almost to the point of being wet - rags in the bores with the pistons halfway down. After the scraping, the shopvac goes into action all around the deck after pulling the rags, as well as on the piston tops.

Turn over the engine by hand for a couple of turns so that any particles that have gotten down onto the rings will be lifted up and left behind when the pistons go back down. Then wipe the bores with a clean, oil-wet rag. When the inside of an engine is exposed you can't be TOO clean.

With the head off there's no better time to replace or at least remove and try to clean out the oil separator box.
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Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.