This is nice stuff. I built a TV-Typewriter using Don Lancaster's cheap video cookbook. He pioneered this technique of 'co-processing' with the 6502. However, if you were going to do this today, you would be better off just building a 6502 into an FPGA [1] or buying an existing design [2] and modifying it. Jan Gray did a nice RISC cpu [3] that clearly got some inspiration from the the 6502 and it was very small in terms of gates (although that isn't such a big deal these days).

It is well worth your time to get an FPGA evaluation kit (my all time favorite is the Altera DE-2) and learn for yourself how straight forward it is to build your own CPU which is has instructions that do things you need vs what the manufacturer thought you might need.

[1] http://opencores.com/project,lattice6502

[2] http://edablog.com/2010/05/06/mos-6502-cpu/

[3] http://fpgacpu.org/xsoc/cc.html

Don's book: http://www.abebooks.com/9780672215247/Cheap-Video-Cookbook-L...