"just using simple chips"

Never judge a chip by its package; eg, take a look at what Cygnal pack into a tiny (3mm square) 11-pin MLP!!

They look to me like Lattice programmable logic devices - you could pack quite a lot of clever stuff into five of 'em!

However, I think that the POST codes on PCI (and ISA, for that matter) are not exactly Rocket Science - I seem to remember it's "just" a matter of decoding certain bytes written to certain addresses; so "all" you need is an address decoder & 7-segment driver?