FYI - The engine number is actually on the block - not the head... So it's not the RB26 they're going to see, it's RB30.
So when you go to vicroads to show them the engine number, they're going to see RB30 + a serial number stamped on the block.
Depending on whether or not the person out @ Vicroads is clued up enough, they're probably going to question the fact the engine serial number that was in there was RB25 and is now RB30.
Good luck though!
Cheers,
matt