I have done two now with L16's, both manual sedans, neither have had anything chopped out apart from the mounts that sit up in the gearbox tunnel, both short boxes, (I think a longer box would be easier as they would be slimmer.

You need to massage (a lot) around where the firewall joins the trans tunnel.

There is a lot of sump work as well, to get it to sit at correct height and angle for the tailshaft, you need to get the sump almost touching the pickup, I couldnt mod the crossmember for IPRA so that caused a few more issues, this is using L16 stanza sump and pickup. L20 is another 3/4 inch higher than my motors, but both my motors clear bonnet by more than that anyway.

Do a search on the wiki, all this has been repeated many many times.