Welcome to Inliners and congratulations and keeping the Chevy II inline. If you are not going to tear into the motor, headers and manifold with either a two barrel or a small (390 cfm)are a great place to start. An inexpensive upgrade is to replace the distributor with a HEI unit from a 75-81 inline. It will start easier and run better with the newer ignition.
You did not mention if the Chevy II has an inline currently. I believe the 68 motor uses a rear sump pan while the early cars use a center sump; if you do not have the pan and pick-up from the old motor, you should be able to pick them up cheap from the put a 350 in it crowd. By the way, replacing the 6 with a small block is not a simple drop in; there are many Chevy II specific parts needed to do it.
For sources of parts, ebay randomly has 6 cyl hot rod parts and Stovebolt Engine Co. and Clifford Performance are a couple of sources for new pieces.
Good luck!
