crank scraper question

Depending on what we're working with.. why would doweling them to the block be necessary when the pan bolts can be the effective dowels.

It depends on the fit of the scraper. Some can be pretty loose. I’ve seen them where the fit to the crank and rods was a bit wonky so to save the scraper and make it fit properly they opened up the bolt holes. A dowel would be a good thing if that happens.

The Teflon scrapers are a self fitting scraper so you install them with an interference fit and they end up where they are which is pretty close to zero fit.