3A vs 3A block

[foxxinabox at wideopenwest.com (Foxx (in a box))]

   i head that a 3A block is a nice upgrade for the JH engine and one 
just uses the stock JH head. my question is why not use the whole 3A 
engine itself? is there a performance gain by using the JH head instead 
of the 3A head? also, i know a knock sensor setup is necessary. that 
being the case, can one simply use the knock sensor from the 3A or does 
it need to come from a 16v PL car? thanx.

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