Thats what they go for. I plan to use the 1983-87 Peizo sensor and ESC module on my '82 GN. The Peizo Knock Sensor run about $35 and is likely better than the 1978-82 accelerometer.
An MSD BTM will not activily protect againts knock. If you ditch the factory system, you can still get a '83-97 knock sensor and ESC module and then use them to trigger a Casper's knock gauge. At least you'll be able to 'see' the knock.