There already exist commercial clones of the 4004, but w.r.t. DIY the easiest way to get to the guts would be through the Verilog version on an FPGA [0]. Alter

There already exist commercial clones of the 4004, but w.r.t. DIY the easiest way to get to the guts would be through the Verilog version on an FPGA [0]. Alternatively you could go full monty and build something like this http://www.megaprocessor.com/ http://www.megaprocessor.com/ [0] http://opencores.org/project,mcs-4 http://opencores.org/project,mcs-4