The first question is, "How much do you want to spend?" The next question, "Which is more important to you, economy or performance?"

The parts you will need to buy depends a lot on what is in the engine you now have. Another consideration is the wear on the engine; can you reuse the pistons? Since it has a 4 into 1 header there is a possibility that a previous owner may have modified the engine. Then again, he may have just installed the header to replace a broken manifold. You won't know until you get into the engine.

I would keep the bottom end stock. Don't overbore unless you must. That way you can reuse the pistons unless they are toast.

Tell your machinist to figure his cuts for a static compression of about 9.8:1. Any higher than that and you will need to pull back ignition timing to keep the ping monster in check.

The B20 came with a D cam and I understand it is a nice cam for the street. (My B18 has a C cam. It works OK but sometimes I wish I had just a bit more grunt.) The D cam will probably return the best combination of MPG and HP. Other cams will make more HP but will sacrifice fuel efficiency. That is a big consideration these days. And, there is no point to installing a larger cam unless you are prepared to do some porting. If you do port the head, the HS6 carbs become the choke point and you will need to consider bigger better air doors.

A stock manifold would help make stop and go driving more pleasant. Since you've got the header and (I'm guessing) don't have the stock manifold, it only makes sense to use what you have.

That would be my plan for a daily driver: a stock rebuild with a slight bump in compression reusing the pistons and valves if possible. Rebuilt carburetors. Electronic ignition. That should give you decent performance and around 30 MPG, maybe a bit more with that OD.

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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 52 year old fat man. ;-)