67 Cuda 273 replacement options

To be honest, I'm mechanically declined in this area. HEre are the facts:
1. Want the engine compartment to be clean
2. Like a bit more horsepower; like to put a little bit of muscle in the car
3. I have 3 boys 15, 13, and 11 that will benefit from this longer term and I don't want any more than they can handle.

Having said that, I'd like to be "all in" at $5k (or less); not sure what it would take to rebuild the existing, but I'm OK with spending some on top of that effort.. Hope this helps.