just read this thread via the blog entry. i am also interested in retro-computing (my 1st computer is one of the early 6502 sbc, an ohio superboard 2).
i am also working on a similar project and thought may be some of u are interested. it's based on the $4.30 ti launchpad and is very compact.
there are no active components on the design (except led modules), leds are driven directly by the launchpad, as well the tactile buttons are scanned.
currently it does a LMC (little man computer) emulation and i am about to finish a msp430 assembler / disassembler (one pass).
it got a minimal monitor to allow for programming editing, 32 segments of 256 bytes of flash are allocated as program storage.
there is may be about 128 bytes of RAM available to execute programs.
i also thought of emulating other CPUs but as the launchpad is not very powerful (i am using a msp430g2553), it will require additional components (like spi ram, etc).
below is a video showing entering and executing a LMC program.http://youtu.be/HNK9imVcz_E
hope u enjoy.