Make your own bleach solution to kill any thing from the mice droppings, recommended recipe is 1:10 bleach to water. These trucks are pretty forgiving when it comes to cleaning. With the clusters out your only other concern may be the heater assembly. Took me three days to clean mine out the first time, nasty job, as it had been sitting many years in a farmers field.
https://www.flickr.com/photos/advance-design_parts_co/8129126615/in/album-72157631867396207/