some exhaust repair questions..

[rochow@pixelmagic.com]

I've got the following parts:
On the car ('84 5000S) there's the pipe
from the cat to the rear muffler, broken off
at the rear muffler welds.
I've got that muffler, with those welds.
On a newly-deposited junkyard
car, there's the amazingly not-crushed-
in-the-ground rear muffler with nearly the
hole length of pipe to the cat, but sawn
off before the flange (so it cannot be
screwed onto the flange on the existing cat).

I'm considering the following options:
IF my old muffler is solid enough around the
"in" hole, jam a carparts store "exhaust adaptor/
joiner" with the thinner end halfway into the hole
and stick the existing pipe from the cat into/around
the other end, tightening the latter with clamps,
while the former would just stick there by friction -

- which makes me wonder: Is there enough pressure
before the regular muffler to push it off 2" of pipe
if I can't get that welded together?

A more likely option would be to get the junkyard
muffler and cut off the overlapping pipe ends
such that cat pipe and muffler pipe meet in the middle
of a straight stretch, and then either stick them into
a flexible hose clamped around them or, if
if there's a close enough match in diameter,
stick them into or onto a hard adapter/joiner 
and clamp down as far as that's possible.

Questions:
-Is the actual inner or outer diameter of that
pipe known?

-Are gauze/polyester patch kits a good idea
to put wround this whole rig-up as a sealant,
or will they just keep additional moisture and salt
in place to accelerate it all rusting away again?
(fire hazard?)

-How bad an idea is any screws whatsoever to keep
exhaust pieces together?

-as I'm probably short on these, what is the
part number on those rubber "donuts" the
exhaust hangs from?

thanks for any help. I guess having the
(not yet synthetic!) AT/diff fluid changed
just made the car too close to fault-free
to last...

-gbr