[retrac]

At that point, you probably do just want to go the path of the LGP-30. The registers are the most expensive part. While you could move them into RAM, that has the same performance cost as an accumulator machine, with more control complexity. If you were considering RISC (without compression, anyway) then you're likely not heavily pressed for code density to begin with. It probably could be done in under 100 gates, excluding the shift registers.