Exhaust manifolds revisited for input

[Wayne64]

I know my exhaust manifold is cracked thru and thru between #5 and #6 cylinder, since I bought it. I have read about others that are cracked also. What is the consensus here on the reason why? My engine has a rebuild tag on it. I mention this in that it may have been a faulty install at the rebuild depot. OR
Is it just a terrible design with the intake bolted to the hot exhaust?
Is it from a run into cold water with a hot exhaust?
Is it from vibration with the secured engine pipe?

With the last potential possibility, what about using the following on the down tube?
http://www.ebay.com/itm/190611296392?ss ... 1423.l2649

[vtdeucedriver]

Worn to missing exhaust clamps................thats alot of unsupported weight hanging on a manifold that heats and contracts. INSPECT you exhaust brackets and if you follow the book on install...............should be ok.

[monkeymissile]

Non-optimal design (too sharp of a bend creates stress risers) coupled with frequent non-use of the correct brass conical washers thereby restricting movement