berg,
for the e30 m3, you can use the e39 525i/530i acs exhaust
for the e24 you can try the e34 acs exhaust
fitment for the e39 into the e30 body is tight, but possible......i have seen it done and heard the note, best mod PERIOD...
for the e24, the pipes into the box need alotta custom work, again, not impossible, as e24 parts are NLA from anywhere......
goodluck