Here is a link to the Jolly page that shows what was available as an upgrade for the light duty Trucks; Clock, Bat-O-Meter and Tachometer.
You could adapt a Big Truck gauge cluster as shown in the link. It will have a vacuum and oil pressure gauge and a mechanical tachometer.
Anything else you have to add-on as you stated.
*I did have an oil pressure gauge in my 61(cluster is different) when I first bought it. It looked like an accessory add-on.
These are all I am aware of or have found.
http://6066gmcguy.com/cluster.html