A Boat Trailer VIN# is either stamped into the Ibeam at neck of trailer (where tounge meets Ibeam) or is stamped on a Vin# and weight plate riveted onto side of Ibeam.
This is one of those questions that no one will will tackle because there are other factors that weigh into this type construction: Angle of lift, How will the new beam be supported, Is the foundation sufficent, indoors vs outdoor ect. I'm afraid we do not have enough information to safely answer your question.
Throw 'em to the lions and tigers. And some pieces go to the alligators or crocs if they have them. Waste not, want not. OK, maybe not, but, that's what I would do. The Prague Zoo has an enclosed aviary with IBeam's and chain link fence to create a pretty big area for scavenger birds. They throw out halves of cattle occasionally, so you see them eating these corpses. Sorta neat, actually