Considering the price of Diesel, and also considering you already have the 454 in there, I'd keep it gasoline. The 496 would be nice though. 450lb-ft of torque at 2800 rpms is quite impressive, stock. You wouldn't have to do a whole lot to the 454. The difference between the 454 and 496 is the longer crank in the 496. So if you're going to rebuild anything, stroke the current gas motor you already have. I don't think asking for 350hp and 500lb-ft of torque all below 4000 rpms is a difficult request from 8.1 liters.

Even though the 6.0L is a torquey SOB...I don't think it'll compare for low end torque like the big blocks.

 

Thanks for the input guys, I have a 6.7 Dodge now and I am building the gas burner for a back up and I will be selling the dodge when I quit working in the field so I want to get the 84 built and restored while i can afford it, I have a 454 i built a few years ago for another truck that i sold before install, bumped the comp to 9.5 or so and thought about the ho cam for the 502. I was considering the 6.0 for possible better economy but from what I have read the 6.0 really wouldnt be any better then the 454 and it would be taxed harder

 

go for the old school BB 7.4 vortec will make plenty down low the mileae might suffer but not much more than a new 6.0. You need to rev the new motors and I still can't get used to that for torque. keep it old school unless your going to tow with this for several years or 100k + miles

 

one more thought if you want to get mileage, switch to a manual trans, I have consinsetly pulled 2+mpg to friends withe the same truck and a auto