I'd take a look at Pioneer's website. There is a post on the 164 FAQ technotes section about installing a Pioneer DEH-P85DHR in a '93L. The poster mentions finding an adapter for Chrysler RD-CH84 on the Pioneer website, but no mention in the radio's docs (he found this out after going the strip & splice route).
I left the stock radio in my 164 as nothing could beat the sound system they installed under the hood in Arese.
Buona Fortuna,