Help me out here.

1. Is the 400 a small block or a big block? (it's a medium block)
2. What does the "M" stand for on a 351M engine?
3. Should I run an external oil line to the rear of the block?
4. Did the 400 ever come with a 4 barrel manifold?
5. How much compression will my engine have if I buy some Aussie heads?
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