Compustar has an accesory you can add to their primary unit. It offers the proximity entry similar to the product you have in your link. But does not allow you to do keyless engine start.
Be careful with some of these retro kits, they require some serious modification including, breaking your steering wheel lock, and removing your ignition key cylinder.
Also not sure if their relays they use to keep the ignition powered up are failsafe non-mechanical relays, as it could potentially cut power to your ignition in case of product failure.
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