Re: What year, good motor?
I agree with Ezeke on the year - the hood decals and paint color sugest a 1975.
One interesting point is that the lower cowl sections appear (paint color) to be from an evinrude. Look for signs that the exhaust manifold cover/plates on the port side of the powerhead were removed. One of the biggest mistakes that people make in trying to do this, is not to pull the powerhead to get the job done. Believe it or not, a lot of these motors end up with holes drilled in the lower cowl because someone was trying to get at the lower exhaust cover bolts. The end result can be that the cowl sections have to be replaced. If there was some sort of work involving removal of the exhaust manifold covers, I would want to know why.
OMC triples of this era were higher compression engines than some of their other models - I would look for compression in the 120 to 140 psi range. If the motor is a 1975, it would be hydro-mechanical, not be hydro-electric. Although I don't mind hydro-electric shift systems, the hydro-mechanical system is a better deal in terms of parts availibility.
If the powerhead checks out from a mechanical standpoint, and the gearbox seem to be OK too, the next thing on the list is ignition. The 1975 motor has the same CD ignition that my 1972 J65 has. What I found with mine, is that I had to replace it all. There is still availibility of parts, but you will want to go with CDI or Sierra parts, because the BRP parts are stupidly expensive. They are also aftermarket parts anyway.
Take a look at the powerpack, timerbase arm and the bottom of the stator, which is visible without pulling the flywheel. If these parts are all metallic (the stator will have a green coating), they are original parts and probably won't last long. If the powerpack is black plastic and the timerbase arm is blue plastic, they are replacements. Same with the stator - if you see white plastic, its a replacement.
Like any old motor, you will just have to give it a thorough look. It could be a great motor, or a total disaster - hard to say from just looking at a pic.