I think for most of us that decision was made by deciding to rebuild an old truck, not looking at it as this piece and that piece .... mostly the final decider at any point is your ability to do the needed work and availablity - it's almost always cheaper to replace something than to hire someone to repair it, and it's almost always cheaper to fix something yourself than replace it, especially as either repro or original replacements will need work as well - if you value your time at the same level as the body shop does you shouldn't be tackling the "rehabilitation" of an obsolete machine, but buying one already done to your taste

Bill