The Byte Attic's Sally replacement adapter is a small daughter-board—using only 5V through-hole technology—which fits into the socket of the Sally CPU in Atari's 800XL, 130XE and 65XE models. It replaces the original Sally chip with a modern, low-power, fully-static, CMOS, currently-manufactured W65C02S CPU, plus some auxiliary 7400-series logic. All components can be sourced from retailers such as DigiKey and Mouser for fairly low prices.
The project has been featured in parts 3, 4 and 5 of Pimp my Eight, episode 6. In these videos, I comment in-depth on the design of the adapter, and you can follow my efforts as I struggle to debug it.
The Sally adapter is an open-source project freely available for download from a repository in my Github page. The PCB's Gerber files are all available there too, so you can order your own board and build your own adapter. The Github repository hosts the complete documentation.
I have successfully tested the adapter in an Atari 800XL and a 130XE. It has worked perfectly. Well-known YouTuber Jan Beta confirmed this in his 800XL, but found problems—namely, annoying image flickering—using the adapter in a 65XE.