Howdy Back IHA68M:
Welcome to the forum. There are lots of ideas here, mostly on the wild side, but, I've always has a thing for the super sleeper. Nothing like having a little six that kicks like a mule. Like with most things, It's what's on the inside that really counts. When all is said and done, make sure to use a stock air cleaner and valve cover, and all the stock fittings.
It would be most helpful if you were to give more info, like what year block and head, what trans, in what vehicle? Are you able to do any of the intensive labor work?
Regardless what year 200- Plan the best head possible! Start with a '78 or later 200/250, three angle valve job, back-cut the intakes, add an exhaust port divider, mill to achieve your goal CR, polish the chambers, add an adjustible rocker assembly,
And build the block with small dish pistons and a zero deck height. Go for as much compression as you can easily manage and take the time to polish the chambers (delibrate repeat!). At least 9:1 actual, measured. A mild 254H performance cam will idle close to stock and be compatible with any trans. The adjustible rockers will help you set the minimum pre-load to get the most out of it.
If you have to have a stock exhaust manifold, use a '68 and port the manifold to a 2" exhaust system with a quiet turbo muffler.
Add a 1101 Autolite one barrel and your looking at least a 20- 30% increase over the best stock running engine.
Depending on year add an early DuraSpark Ignition from '74, with stock, small diameter, plug wires and coil for a fool-proof, stock appearing system.
Lighten the whole rig, with an appropriate trans and rear gear, say a T5 with a stock shifter and a 3.50:1 rear gear, and you'll be the big surprise of the stoplight Gran Prix.
Thanks for the opportunity to dream.
Enjoy!
Adios, David