I love notchbacks and convertibles. Welcome! I followed the following path and lived with a slant 6 for 10 years. I finally was done with it and went the 5.9 Magnum route.
I would highly recommend upgrading the brakes and wheels to a big bolt pattern. Brake upgrade being the most important system to prioritize. Followed by suspension and the big bolt pattern (BBP)wheels.
Dr Diff can set you up with a four wheel disc brake package, a BBP upgrade and a suspension upgrade. Invest in some good shocks (Koni's or Bilstiens) and weld in subframe connectors from US Cartool while you're at it.
Once you have a car that stops and handles dramatically better, then go for EFI & an overdrive transmission and you will have an awesome ride that can out perform most cars on the road.
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