Converting the throttle/gear from single stick to dual stick (gear and throttle)
 

A friend of mine has a boat with the mercruiser single throttle stick that also puts the drive in forward and reverse. He wants to convert it to more of a offshore type setup like I have on my boat (gaffrig). Is this a difficult conversion? Do you use the same cables or do you need to buy new ones specific to the new offshore controls? His trim is also in his handle. Is this is simple conversion as well??

I did a search because Im sure this has been discussed previously but couldnt find anything.

Thanks!!