My old text makes no mention of scrolls, none in the entire text. It shows a heated expander and a cooled compressor connected by flows through the regenerator, and briefly explains the Stirling cycle (with p-v and T-s diagrams). It seems that regular pistons were assumed instead of scrolls.
As I understand scrolls, from diagrams, animations and texts from the internet, they are an ingenious way to compress and expand a gas. Their efficiency is a function of how perfectly they are built to match the mathematical curve. With a tight enough tolerance (and/or use of a sealing lubricant) very high efficiencies are possible. But looking at modest power production and plenty of space in a stationary application, and with a substantial heating load, low efficiency (even very low efficiency) works for me.
We have a high temp and a low temp, what is the simplest effective heat engine we can build? Maybe it involves two scrolls and a regenerator? Maybe it is not technically a Stirling?