Re powering from twin 70's to single 150

Bought my 1986 18' Boston Whaler new in 1986. The twin 70hp Yamaha's have never missed a lick in over 3000 hours of use, both in salt and fresh water. That is until last week when I lost power in one, she didn't quit on me totally and got us back to the dock. Upon further examination found that I lost a ring in the center hole and it scored the liner real deep. I can't afford to re power with new four strokes like I would like right now. A few years back I bought a 1990 150 Prov at an estate auction. More like stole it actually. I have gone though it pretty well, bench ran it and all systems are go. I was told that it less than 700 hrs on it and from the looks of it, I believe it. It will have to do for now at least, the season has started at Pyramid Lake NV and I have to get back out and catch some more of those 20lb cutthroat trout.

Now my question: Will I be able to use the controls, wiring, instrumentation and trim from one of the 70's or will I have to buy all new. I can't even express how much I don't want to have to change all the cables and wiring because it goes all under deck and you have very little access to it.

Since I never got a reply to my question I just dove in and changed the motors out the twin 70's for the single 150. Here is what I found. The ten pole wire harness plugged right in and worked except the tack reading is wrong. The main power and ground had to be wired in a bit different and if any one needs to I'll go into detail and post a photo. The trim remotes and gauge and auto choke all work. I was able to use one of the steering cable no problem I just removed the second one. The biggest hurdle to .jump was the throttle control linkage. On the 70 hp motors they require the cable to pull to accelerate. On the Prov 150 hp it requires the cable push to accelerate. Since I had two sets of cables I used the gear shifting cables of each control, and took the throttle control cables out. One control handle now engages the motor forward and reverse and the other advances the throttle. Also the cable ends needed to be drilled out a 16th of and inch to fit the pin. I had to custom make a way to hold the ends of each cable also and did so. (Back yard engineering style.)
Long story short took it out today and it worked perfectly mechanically, except the tack reads double what it should by my guess.

Is there a switch on the back of the tach? If so try different settings and check it with a timing light tach.

well done Cutthroat

Thanks, I did find a slotted adjustment dial under a rubber plug on the back of the Tach. When turned with motor running it only seems peg it to 7000 rpm idling and off. I have been trying make sure the tach is compatible with motor but not having any luck finding that data

Thanks so far so good, just gotta get the tach figured out.