Many years ago some friends and I had a weekend to block swap a turbo d16 civic that shit the bed and the only d16z6 we could find on short notice looked like this.

We picked it up friday afternoon. Scraped out what we could get to and filled it up with a mix of equal parts diesel, auto trans fluid and acetone, sat a radiant heater under the oil pan and got drunk while we cranked the block over with a rattlegun every few minutes, we drained and refilled twice but the internals came out surprisingly clean and the block did take about 18 months of being wailed on before it died.

If it insta-dissolved the crud, that would be great, but it'll probably just loosen it and clog up the oil galleries. I don't put much trust in Seafoam. Anything that's supposed to fix so many problems probably doesn't fix any of them.