First of all the difference in Hp will be noticable expecially if you run normally at max speed. The 130 is heavier and less HP, so the performance is lower, but should not matter is you run mostly at cruising speed.
The fuel consumption on 130 will be two to three times better than the 150.
It also will be so much more quiet and you will be able to talk (and not scream) over the engine sound.
If you do it, you should change out the shifter, key switch assembly, and associated cables. Can the Mercury stuff be used?....yes...with several wiring changes and a change in control cables to Mariner cables, however, it will not shift as smooth and in the end, I do not think you will be happy.
As for the gauges...it depends which gauges you have. Depending on the vintage and brand, the gauges such as volt meter, fuel gauge, tachometer (in many cases - depending on the settings on the back), and water pressure gauge (if it has one). If you have a temp guage and a trim gauge...they are not compatible with the Honda.
If you go for the Honda, install the Honda key switch panel that has 4 warning lights (oil pressure, check engine, charge light, and overheat).
The other thing you do have to check is the steering. If you have hydraulic steering, the cylinder may or may not be usable without modification.
I think I covered most of the major items.
Hope this helps.
Mike
