Big blocks are truck or if your building a drag car thats primarily just a weekend track toy. The engine just weights a ton, it will effect the handling of the car with the added lbs in the nose. Plus they suck down the fuel. I had a 2001 Chevy 2500HD with the 8.1L V8, 340HP, 455lbs-ft of torque. Fuel economy was ok at 13mpg unloaded at my best. it was just a regular cab 4x4 with the 4.10 gearing. Winter got about 11mpg, towing heavy I saw 7mpg.
You could build a nice small block with a decent about of power, you get good fuel economy, good handling due to the lighter weight. Great for a street car and in the older cars which don't have great handling. Nice car btw, I would love to get a project going.