Well it can't be any longer then the block! That is the biggest.
You need to stay with a mild cam. The big heavy truck and tires need the low end power. I don't know 350 cams but you can't put a big nasty cam that will loap. I had this dilemma when I put a cam and intake on my old ford. I wanted big, choppy, high hp but you can't because the truck won't leave a stop light. Look for cams that have a rpm range of 1000-1200 and most of them will spin to 5500 or 6000. Then do like I did and plan someday to make a high hp motor for a car or light weight truck down the road. My plan is to someday build a 1000 hp motor. It will happen also.(see what happens when you are forced to use small rpm performance parts.)