The E30 dashboard predates CAN bus by a decade. To run a B58, you must abandon OEM ECU entirely.
ECU Options
Choices: Link G4+, MaxxECU, or Haltech Elite 2500.
Pedal Box
Mill down pedal boss or fabricate custom 6061 aluminum extension.
Wiring
Fabricate standalone harness with 18-gauge TXL wire. DIY: $600 parts + 40 hours.
Difficulty
Rated 9/10 — only attempt with harness experience.