JaN,
We put a 350 in our '54. We had to fabricate new motor mounts, but that was about the biggest challenge. Later, we had to put in a 305 when the 350 went out. We put in the 305 because we had a donor truck to pull it from. It was a pretty straightforward swap. We were able to use the same motor mounts we fabricated for the 350 on the 305, so you'll be able to upgrade someday if you want to.
Everybody's got an opinion about what to do with your truck, which is cool. Just remember, do what makes you happy and have fun with the project. It's YOUR truck!
-K
