4000 cracked manifold

[Derick Farfan <bg18461@binghamton.edu>]

I just came back from the mechanic.  He changed the 3 bolts that
surround the cat. convertor in my 85' 4000s(fwd), they were hanging
loose and completely rusted.  They made this annoyingly loud sound while
driving.  Replaced bolts, but there is still a sound.  It turns out that
I have a crack in my (CAST IRON) manifold, go figure.  My question is
since I have to change it anyway, should i possible upgrade to a better
manifold, power wise.  Or should i just replace it, I have another
4000(86) as my parts car.  It has a good manifold.  Should i just take
that one, or upgrade.  I have a sport tuned rear muff, but i need to
change the front muffler, any suggestions.  I figure i will change all
the pipes from the cat back while i change these parts.

Any response would be appreciated.