pretty much as you describe, i understand the atessa (located in the rear) takes an rpm and speed signal from the ECU.
the issue for me will be can an R34 powerFC be shoehorned into the stagea, still waiting for a copy of the pinouts to send to the tuner to see how hard it will be to modify one. i prefer the powerFC due to the overwhelming support of them/currently use one on an R33. however, if i get stuck i am looking for a decent alternative.