I believe you can swap the pumpkin from a later model into your truck but it has to come from a 3/4 ton. I dont think you can use a 1/2 ton. Others who know more about this than me(almost everyone) may answer your question better.
Good luck.

"Do not walk behind me, for I may not lead. Do not walk ahead of me, for I may not follow. Do not walk beside me either. Just leave me alone, you're starting to freak me out."

1957 GMC 150