I'll chime in as MBHD suggested.
I have a 69 Buick Special Deluxe with a 250 and I use a 4 speed saginaw tranny behind it. I think for your money, a turbo would be the best route over the naturally aspirated. There's plenty of help here for a turbo build and I think the possibilities for a turbo engine are better. It'd be a nice mild mannered engine driving everywhere and then it'd be a lightening bolt when you spool up that turbo! Also a mild turbo build requires minimal machine work and the overall cost would be similar (I think)
I built a turbo 250 for around $2000. That includes
-HEI
-Holley 500cfm 2bbl Carb
-Carb Hat
-Turbo/Wastegate/BOV
-292 Exhaust Manifold
-Offenhauser intake
-Turbo Piping and flanges
-AEM Wideband Sensor and gauge
-Boost gauge
and haven't used it yet but also my new fuel system which was about ~$500 of the total cost is
-8 gal fuel cell
-Walbro 255lph fuel pump
-Mallory fuel pressure regulator
Here's some pics of my setup
