You can replace the diaphragm springs with coil springs, much like valve
springs but much smaller diameter, to allow movement of the J-pipe
connection.  Of course, longer bolts will have to be used to accommodate
the longer springs.  I've used this on the J-pipe on a Subaru conversion
with much success.  The springs came from a local hardware store and I
tightened the bolts until the springs were just before "coil lock".  The
iron donut works like a ball and the joint is now actually a ball joint.
This flexibility allows very easy assembly of the exhaust system without
stress.  I have seen absolutely no soot at the joint that would indicate
exhaust leakage.

This joint also reduces the amount of harmonic vibration of the exhaust
system by allowing more flexibility than the original diaphragm springs.

Here is a link to the SubaruVanagon yahoo list picture.  Scroll to the
right to actually see the correct picture.  I have now used this for 8
years without problem.

https://groups.yahoo.com/neo/groups/subaruvanagon/search/photos?query=j-
pipe#zax/albums_1825126794