Depends on where you live ina colder or warmer climate and how many miles are on engine. But a good start would be in the 10w30 -15w40 range.
If you missing oil faster than you like you could move up to a hight weight oil, I know that the 454 seems to consume oil no matter which weight oil is used even on very healthy motors. I do not think you need 20w50 though. But if its very healthy motor you can get away with 5w30 or lighter but watch the oil level and see if it want to turn dark too fast and keep it change before getting black. If your using thin oil and it turns dark fast or is being lost due to consumption try moving to heavier weight, and if using thicker oil and it turns dark too fast try lighter weight. Also on the 454 if you have not already or not a OEM cooler in radiator I advise using an external oil cooler.
Welcome, and a oil filter relocate adaptor would not hurt none to make it easier but is not a have to do thing but I have noticed that if its easy to do then it gets done more often. Sometimes they tend to run warm (those from the 70's). If yours does a high capacity radiator will cool things down.
Thanks again for all your info. very helpful.
10w30 in the cooler half of the year. 15w40 in warmer half of the year. If its not below zero but a few times a year. 15w40 is fine on healthy motor and 15w40 if it has many miles, and 20w50 if its smoking. Also if you have more cooler days where you live and a short spring & summer, 10w30 or in even colder climates 5w20. I think with the 454 consuming oil fast on its own the 0w oils will disappear too fast even though it will run fine with it if it does not show smoke out the tail pipe, it will disappear, meaning you will need to keep quarts of oil just to top off with on-hand over the normal amount you already need to top off with in-between oil changes.
Looking for a Used C/K 2500 in your area?
CarGurus has 2 nationwide C/K 2500 listings and the tools to find you a great deal.
Search Chevrolet C/K 2500 Questions
Chevrolet C/K 2500 Experts
Related Models For Sale