More than likely 5 quarts with filter change which was the norm for almost all engines of this era. Park the vehicle on a level surface, drain the oil and replace the filter. Add 4.5 quarts and then start the engine and let run for 2 minutes. Shut down and wait 30 minutes. Check the level and add if necessary. I suspect you will find it to be 1/2 quart low.
While owning a vehicle is important to know the engine oil capacity. In a 1991 Chevrolet Silverado truck the oil capacity is five quarts of oil with the filter change.
5 quarts.
Engine oil with filter change 6.0qts
5.75 quarts with a new oil filter
The oil capacity of it if you're just draining the oil and changing the filter is 5.75 quarts.
7qts
Its 6.4L if you change filter also.
5 quarts
6 quarts
5 quarts
4 quarts with oil filter
Depends on engine. The common 235 six has the oil cartridge in a tin lookin can below the carb.