86 300zx ready to have changes made to it

I have a 86 5 speed 300 zx that has set at my parents house for the last 3 years...and now I am ready to make some changes to it. I am thinking about having my mechanic to put a bigger and better engine in it.. what engine would be an easy upgrade for it. I plan on also having it painted soon...The leaves and back yard plants have caused the paint to look bad. Also I will have another clutch put in it. 3 years ago..I knew my clutch was not at it's best...so I will have that change too.. So since I plan on doing some work to it.. I figured I might as well make it faster at the same time. So again.. what kind of easy engine up grade can I add to it and possibly what kind of clutch system should I look for in my 86 300 zx.