Plenty of people have done L67 swaps into non-supercharged 3800 applications. The main things to consider:
1) PCM tune. The Park Ave & Lesabre still use the 4T65E transmissions which means there are differences between the two in gearing. Also the fueling tables are different between boosted and non-boosted applications. ZZPerformance sells a box tune pcm that would fit your application. Just make sure you check the right boxes. The other option is to find someone experienced with HP tuners or DHP powertuner to do a custom tune for you.
2) Differential. The Lesabre will have a non-HD diff which will be susceptible to grenading itself if you tend to launch hard. You will need an HD diff & HD axles. Something to strongly consider.
3) Harness. Yes you will have to do some wiring work upon your swap. ZZPerformance sells an L67 swap harness kit with a map sensor connector extension & supercharger bypass connector.
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