What an amazing little machine - and they managed to build it using (a lot of) standard 74-series TTL chips and a few more PALs than the original Mac uses. The board picture on bitsavers shows ICs with date codes between 1980 and 1984, so it's a bit hard to say when it was designed/built.
It seems that the CPU still runs at the original 7.8336 MHz (oscillator U285) and it doesn't seem to have separate video RAM. In addition to the 1 MB DRAM (32 x Fujitsu 81257 256kBit chips) there are only 2x2kB 45ns SRAM for the MMU and another 2x2kB, which I assume are used for the color LUT.
I wonder how they managed to squeeze the required bandwidth out of the design without significantly slowing down the 68010. The DRAMs feature a fast "nibble mode" allowing for high-speed access to four bits of data, but I'm not sure if this makes a lot of a difference. Do you know if the YACC used the original 512x342 classic Mac video resolution?
