JDM cat back compatibility

hi all, i have a 95 dc4 and need to replace my cat back soon.

ive seen some jdm catbacks for sale, mugen twin loop and spoon n1 but after reading on some other threads and found out that theyre not just bolt on.

i know there is a difference with audm and jdm exhaust systems
audm type r 450mm and gsi/vtir 300mm
jdm type r 300mm (could be wrong)

1) first question is does that mean the jdm cat backs will fit with no gaps because the cats are same size?

2) second question is it might be cheaper buying a type r full exhaust. so i want to ask if type r headers are compatible with b18b engine?

thanks any help to steer in right direction would be appreciative

I know this thread is old, but just in case if anyone wanted the answer..

When the mechanic installs a new exhaust piping (whether its the cat back or the header), if the pipes are of different sizes they put in what they call a 'flange' and this ensures that the two pipes connect directly to each other. Different flanges are used for different set-ups. So in a sense, there shouldn't be any gaps, but your only problem is back pressure

e.g. headers = 450mm --> cat back = 300mm ... then you'll experience what we know as bottle necking (good low end, crap top end)
headers = 300mm --> cat back = 450mm ... then you'll lose most of your back pressure (crap low end, good top end)
essentially the best set up is to match the pipes (e.g. headers & cat back = 450mm).

for the second question, the only thing you'll save on is the flange which is less then $100 (from memory)

hope this helps, and if anyone can correct me.. please do. =)