Whether you do it yourself or not would be determined by your abilities and/or experience and or availability to tools/shop.
First get yourself a book like How to build a small block chevy. David Vizard writes great books. Well worth the money. Here is a link.
http://www.themotorbookstore.com/chevy-small-block.html Double check the engine casting numbers to make sure you have a 283. Check the head castings to make sure you have a matched set. Find a machine shop that will spend a little time with you. You can rebuild your oil pump and run it in most cases (even though they are cheap to replace).
I think I would rebuild it with the heads you have and drop an RV cam in it. If you are looking for mileage, keep the carb small (350 to 600cfm max.) Bigger is not always better. In your case I would stay small. Don't listen to the parts house guy who says his buddies friend runs a 750 cfm Demon on his and he has so much HP blah, blah blah.
Maybe find an HEI ignition for it (although your stock points will probably work fine). A new HEI can be had for less than $150 from a warehouse supplier like PAW.
If you don't have a stock manifold and carb, an edelbrock performer and an edelbrock Q-jet carb would be fine and probably run pretty close out of the box.
Also, I wouldn't wast my money on forged pistons if you are replacing them. If you want to get mileage, cast pistons will be fine. Also keep in mind that the parts for the 283 are more expensive than a 350. If you think cast pistons aren't good enough, go with hyperutectic like Keith Black's. They can handle up to 400 or so horse. You won't be hitting that. That is why I said to save your money and get cast pistons.
I would say htat dependability is great from the factory. So, if dependability and mileage were your goals, stick to stock and forget about all the horsepower "advice" you will get. Keep it simple, especially for your first build.
Good luck, keep us posted.
