transom/engine question

[SonOfABeach]

What would be the negative of rebuilding the transom, and getting a bracket or jack plate for a 20"? What would be the benefit of having a 25" on a bracket or jack plate with a closed transom vs a 20" on a bracket or jack plate with a closed transom?

If there wouldn't be a difference then when I repowered I'd just put a new 20" on it, vs modifying my current engine and then buying a new 25" engine.