[Old65C10]

Welcome.

It is always a risk to take an engine that has been sitting for years and try to start it up. I have seen everything from just turning it over by had before firing, to filling the cylinder with oil and letting it sit for a day to a week.
At a minimum, you will want to change all fluids. Turn it over by hand at least 2 full revolutions. Pull the distributor and use a oil pump primer in a drill to push oil through the system.
Put in new spark plugs and try to start it. If it runs, you can decide if it runs good or not, do a compression test. See what the overall health is of the motor and go from there.
I have a 1965 C10 that I got running after sitting behind a barn for 22 years. It runs great now and I have not pulled the engine apart at all. But every case will be different.
Time does bad things to seals, so don't be shocked if the thing leaks from every place that hold fluids.
Transmission, brakes, etc. are all another story and need to be dealt with.