They can be loaded onto boats by building out a platform and knocking out the floor below them, but it's risky. Harpoon and friendly fire mode is the simplest approach.

Big distances on earth ? U cant
To another island ? Make some stairs platform in a shore, and make them fall in your longboat
I only did it with wolves , not with boars

A large step up portal that required 3-4x the mats a current portal uses would be awesome.

Lox with warp drive

I populated my world with 2 star wolves by harpooning them and then towing them through the water with my longboat. Never did run into a serpent I bet the 2 star wolf would have kicked its butt.

If you link up a big and small portal would you get an ACME Industries style shrinking tunnel?