I’ve always wanted to get one of these old Apple Newtons and trying to upgrade the built in handwriting recognition system with something a bit more modern, within the limitations of having 8mb of ram :). Anyone have any experience hacking them?

I think it would be more interesting to run under emulation. The hardware is getting a bit old and creaky these days. Under emulation it could enjoy a considerable CPU and RAM boost.

An iPad with a pencil would be an ideal target.

(Given that it uses an ARM processor, maybe you wouldn't need to emulate it, on A and M-chip devices.)

You need to locate the ROM. The Internet Archive has some: https://archive.org/download/AppleNewtonROMs