318 head cleaning question

If you have a lot of sludge on the heads, then likely there is a lot of sludge inside the rocker shafts. So I would be planning on pulling those off, knocking out the end caps and cleaning the shafts out and getting new end caps.

And I would not ever power wash a head without immediately pulling it all apart. Who knows what you will jam into the guides and under the rockers, and inside the rocker shafts, in addition to water and detergent and the resulting rust. And I'd bet the power wash force will wipe out the old and brittle valve stem seals and those needs to be replaced by now anyway.

BTW, if you have a lot of sludge in there, it cold have been the old Quaker State or Pennzoil oils; they had a lot of paraffin in them. But, it could also be due to a slow fuel leak from the carb or fuel pump into the crankcase. If it was a carb leak, you may have some badly worn cylinders, as a slow carb leak will repeatedly wash down the oil from the cylinder walls.