Peter Williams asks how much for a six.  I paid $1500 for a partially 
assembled 2.2 liter, including the oil tank, and have never seen a better
price for a complete engine that was not being sold as parts.  You can find
lots of good engines in the $3000-$4000 range.  And you can pay $10-15k and
not be wasting your money, depending on what you want.  Don't buy less than
a 2.2 liter (due to age and 2.0-1.7 is only .3), be wary of 2.7 liters (but
I bought one, knock wood), and keep in mind that any Porsche engine holds its
value real well.  Even a basket of parts is probably at least $1000, and the
3.0 (78 and later) engines routinely go to 200,000 miles with good care.  Read
lots of books.  See the FAQ on porschephiles-request@tta.com.
B.