Short block is a partially assembled engine it requires alot of parts to run. A long block is a partially assembled engine that requires some parts to run. When i say some i mean it needs a skilled mechanic, cleaning your old parts from an existing motor or buying; valve covers, oil pan, timing cover, intake manifold, water pump, distributor and a bunch more, you gotta set the timing, all that crap. If you can't built a motor don't buy one of those. Buy a turn key motor, it's ready to run outa the box, has been tested and ran, timing is set, has EVERYTHING! Just needs a home.