I know we are having a good thread dig here but here’s my thoughts anyway.
To my mind the piston slap is a design flaw of the engine because GM designed the engine with piston skirts that are too short and too narrow. The narrow and short piston skirts act like a hammer hitting the piston wall.
When you look at pistons for other engines (I looked up Holden 304, Toyota 1JZ and Nissan RB26) they have long and wide piston skirts to locate the piston correctly in the bore. It still amazes me that GM never bothered to fix this obvious design flaw by extending and widening the piston skirts.
This would have cost them effectively nothing in the great scheme of things (a few hundred grams of extra aluminium per engine) and improved their reputation in the market but I guess when your always getting bailed out by the US taxpayer anyway who gives a shite about actively improving your products to compete with the rest of the market.