I'm still not sure, off how much use those old sources would be today ..
Just downloaded the TPaint-sources, and found 2.6MB of sources, all
of them in 68k-asm (except a tiny arexx-thing which is in C).
Also probraly pretty much relying on old obsolte HW (the Amiga-Chipset,
and the orginal VT). I fear a port to normal GFX-cards and/or the PCI-VT, plus
the much needed conversion to C would be no less than a complete rewrite.