I've seen a lot of discussion on making a CPU from TTL or MSI (bitslice). The task is not that bad and the parts to do it are very available still. The assembly task with out a premade board can be large as it's a lot of repetive circuits. If the word size is kept reasonable but useful and that seems to be 8 to 16 bits people are doing it. The variable word length 8bit designs are scarce but requires less bus "width" to get a workable system and have performance in the zone of faster than serial but not as fast as wide word machines. Using that approach you can have a 32bit machine with 8bit busses saving a huge amount of repetetive hardware. For those that want small and less significant part counts there are minimalist 8/12/16 designs like TOY or Pilgrim VSC (very simple computers). A board for one of them would have wide appeal and useful for those that wish to see the guts of cpu without probling a die or having a whole PDP-8. The biggest difference between building a PDP-8 (or whatever) then and now is not using TTL (or cmos) or bit slices but the availability of fast and large RAM that is easy to use. Many earlier systems were flavored by the ram they could interface or the needs of the memory. Same for the older serial designs to were done to economize on then costly registers and arithmetic logic along with serial memories. There is a lot of "you can do" but building a CPU comes down to what do you want to do and can reasonably achieve or can practically play with once functional. Unfortunately some want a cpu that can run unix and an IP stack others want just enough to qualify as a computer for close up examination of "just how do they do it?" and that represents a large spread of design and architecture possibilities. Having built machine all are interesting but some are a lot too much work. Allison