There were a couple of posts on the 240 BB a month or two ago on this. One guy had used the IPD kit and was happy. You do have to pull the driver's door apart to install a lock/unlock solenoid and run wiring from it to the relays...other than that it should be straightforward.

I went the junkyard and elcheapo keyless entry route for the 83 240. Got lock solenoid, wiring harness and linkage from a wreck, 'black box' and remote transmitters from an internet supplier. The setup allows for driver's door 'priority unlock', then the others with a second press on the button. This required some thought about wiring and an extra relay, but works as intended.

For an ugly old guy like me the remote unlocking - particularly the driver's-door-only feature, is just a neat gadget and convenience, but for my wife or daughter, alone in a nighttime parking lot and wrestling a big bag of groceries, it could be a security feature.

If you are interested, I designed the circuit as an Excel drawing and can email.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and numerous old motorcycles)