Replacing leaky pre-muffler/emissions

[sjagernauth@attmail.com (Stephen I Jagernauth)]

Picking up on the exhaust thread, I have a leaky pre-muffler (ahead of LR 
wheel) on my '87 5kcst.  The car feels as though it has a clogged cat, low on 
power, very sluggish, takes a while to spool up.  Would this leak cause 
increased back-pressure leading to these symptoms?  What is the function of 
the pre-muffler, other than muffling?   Can I replace with a straight pipe, an
aftermarket muffler or is it part of a tuned system so it should be replaced 
with the OEM part?  I have a new rear muffler and the rest of the exhaust is 
in good shape so I'm not inclined to replace the whole thing.  

In Easton, PA, starting recently, we are exempt from emissions testing based 
on zip code.  I was surprised when even the modified motor in my 911 passed 
last year without a cat (no cat req'd for '74).  Is there any value on having 
the emissions test done anyway to catch a possible problem? 

TIA,

Steve Jagernauth
'87 5kcst wounded
'88 5ks 
'74 911/3.0