Another vote for the 5.9L Magnum swap. I did one years ago on a 87 Ram D150. With headers and a carb it was a solid 14 sec truck.

It may take a slight bit more work but you should seriously consider a late model 5.7L Hemi swap. With a 4 barrel carb intake and a aftermarket fuel injection. You will have a lighter 400hp engine that will get better mileage than any Magnum or old LA small block build.