I have used solvent flushes three times on old, dirty engines.

Each time, I have had lifter problems some time later.

I think that this is because the top of the engine drains down through the lifter area.

Once, I used an old shop vac, a crevice tool, and a scraper to clean the top of the engine. This actually worked well.

The next time I try to clean up an old engine, I will clean under the rocker cover, than install a new filter and detergent oil.

When you change the oil, try to drive the car up on blocks or ramps to tip the car so that the sump drain is low and make sure the oil is hot, you will get more gunk out that way.