i love your car. the hatch style is these cars is very unique. also. i think that swapping a ca would be the same as a ka in terms of the amount of work you have to do.
i have been thinking for awhile about this swap. have you every considered swapping in a vg30dt? from a turbo 300zx? or even just a naturally aspirated vg30d. if you are going naturally aspirated, i would go for as much base power as you can. but if your dead set on a ka, then get the dual over head later version.
or if you have the cash and fab skills, why not a vg30de from a newer 300 zx. that whole swap is like 1500 bucks