Ganesh, is is power, or speed that you are looking for. The old final drive could be changed to give you better speed.
As Mobile stated, a V8 and overdrive transmission would be a good swap. These are plentiful as 305's and 350's in many '78 and later vehicles. Even a 250 / 200R4 combination would feel peppy.
If I were in your shoes with a running truck, I would follow something like Cosmo and put in a T5 hybrid and different final drive, then drive the truck, adding intake and exhaust items as needed.
