~$500 sounds like too much

you may need to bypass the neutral safety switch if you are using the auto harness

the oem ecu will go into default mode unless the s13 speedo is hooked up, but maybe you can find a shop to tweak the ecu

swaybar should work since both oil pans are front sump. the problem is with 510s because they have rear sumps

I don't think there's any room on the manifold side, but you should talk to datsuns.com guy about clearance issues on a lhd 1200