I'm a firm believer in the "If it ain't broke, don't fix it" philosophy when it comes to antique cars.
On one hand, you have a perfectly running engine already installed in your truck and you say you don't need more power.
On the other hand you have an engine that is essentially a "rebuildable core", regardless of the seller's claims. Even if it was "running when pulled," 50 years sitting in a garage didn't do it any favors.
You can either open a large can of worms, or be happy with what you have.
