What exactly are ther differences between a Bravo HP transom assembly versus a stock bravo 1 transom assembly. What changes are required to retrofit a bravo HP transom assembly to an older Bravo 1 drive.

HP has stronger hinge pins. You will not have trim gauge or trim limit, have to use mech. trim gauge.

You are wanting to go from HP to standard? I think there should not be any problems changing except for trim gauge & limit.

Not true anymore about the trim gauge or limit. It now includes the same trim sender and adapter included with the ITS.

I have to correct my statement: It's "available" with the sender. They also sell it without.

Thanks - I want to go from a standard to an HP so it sounds like the only issue I'll have is the trim sending units. Sound correct?

That should be the only difference. Some dealers may not be aware that the HP is now available with the trim sender. You can add it to the later ones because the mounting points are there but you have to purchase all of the individual parts. It's much easier to order it the correct way.