I wouldn't bother to update the design much, if any.  The only good
reason I can think of for building such a thing would either be for
nostalgia or for classroom education.  When I say education, I mean
for teaching the basics of how the internals of a computer work to
engineering students since the 8-bit systems like the C64 or Apple II
are so much easier to understand than a modern PC.  Now, the Apple II
was never my area of expertise (I'm a Commodore fanboy) but if I'm not
mistaken the Apple II was designed from all off-the-shelf parts,
right?   So it should be possible to still build one today with off
the shelf parts.  I'm surprised nobody has come up with a new board
design.
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