Adding a modern ATA drive (IDE) to a vintage computer is a very
practical project.
I'm running 20 gig ATA drives on an HP1000 using a home made controller.
Its almost trivial if your not
too concerned about performance, and only mildly interesting if
performance matters.
By far the hardest part is developing a driver for your chosen machine
and O/S. The ATA control firmware
is available freely.
Grad a wire-wrap board for your machine and do it!