You need to build your engine based on what amount of power you plan to make and how you intend to use the car. The heads, cam, intake, exhaust and fuel system are the power adders. The short block is just the foundation. Depending on what you select you may need supporting mods, like motor and tranny mounts, torque strap, upgraded coolers, tranny, clutch, converter, driveshaft, half shafts ect...
For example if your planning to build your engine to run high to mid 13s you can use stock pistons and rods with bolt-ons. If you are looking for a high 12 second or quicker street driven, stock weight SC, you will need better rods and pistons, heads, cam, a spare car and on and on.
The stock crank is all there is, unless you offset grind it for more stroke (needs custom rods and pistons) or buy a custom made crank like Fred did (big $). Balancing is manditory and an upgraded dampner like the BHJ is also reccomended.
If you want to know what mods people have, go to the top SCs section and click on that person's member page. Most have plenty of details listed.
David