The radio harnessi is easy for your model. Use a BT ISO DIN version to wire to your new radios pigtail.
The speakers might be harder to tell size without reomving at least one. My chart shows Kenwood used a mixture of 5 1/4, 4, and 6 1/2' speakers. Usually smaller spekers were overhead.
SPK link https://www.bigrigstereo.com/speaker_application.html
Harness: https://www.bigrigstereo.com/kenworth_radio_harness.html