Re: what parts can i use
As Nordin said, everything is interchangeable. The 85 does have larger venturi carbs and larger jets BUT-- horsepower is limited in these 3 cylinder engines by the port timing and size. SO: even with the larger carbs, you still will net about 70 HP at the crankshaft.
The 70 has circular exhaust ports, 1 3/16 diameter venturi WB carbs, but prestty much everything else is the same. The 85 has elongated exhaust ports and 1 5/16 WB carbs. I believe that the 70 is also limited by the reed stop plates. I think they are set narrower to limit reed opening. Again, changing them without other mods will not affect horsepower much, if at all.
NOW: How serious are you about "waking-up" your 70? It can be done, but there are no quick bolt-on modifications. You must disassemble the engine and do port work. The first two photos show porting done with a drill press, the next two show a 2 cylinder engine done by hand with a Dremel and carbide bits. note that only the bypass sides are shown, but, the exhaust was done essentially the same.
One thing that MAY help is if you can find a 2 to 1 ratio lower unit off a 90 HP. But, you have the 2 piece lower unit and they are becoming rarer than hen's teeth.
