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.
5.75 quarts with a new oil filter
Engine oil with filter change 6.0qts
The oil capacity of it if you're just draining the oil and changing the filter is 5.75 quarts.
Its 6.4L if you change filter also.
5 quarts
5 quarts
7qts
6 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.