I've got a 97 12 valve parts truck with a p pump. I could use that motor in the 68 if I wanted to. But as far as putting in a p pump to replace the VE in my 93, I can't get it to burn all the fuel I'm throwing at it now. And I currently have the VE pump power screw set at almost the stock setting, and running 5 x.012 injectors. Before I put in the injectors, I had that power screw turned in 2 full turns, it was amazing how much that woke up the truck. Even when I had the stock turbo on it. If I was to crank that screw in now with the bigger injectors installed, I'd either need a bigger turbo which is going to have lag and smoke on the low end, or switch over to a compound turbo setup. Which is definitely a possibility. Or else find a 6.7 to put in there. I like the idea of the exhaust brake on the 6.7. But I could always add an aftermarket exhaust brake on a 12 valve as well.
I'm just trying to weigh out my different choices.