First of all going from twin 150's to twin 115's wouldn't be a problem apart from it would be slower, It was originally designed with a maximum of twin 200HP, the boat would weigh roughly 2700-3400lbs empty but twin 115's would push it along nicely.
For fitting out, are there any control boxes or engine harnesses left, if so they may be utilized but if not does the Yamaha's come with controls etc? All that has to factor in the cost of refitting charges. As for price on engines of that era, i'll get back to you.
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