They have LOTS in common with the later XU 16v engines, I'm guessing you also posted on the 205 forum? there's a TON of info on there about these.
Cam ladders are the same casting, smaller tappets other than 180 engine, same cam blanks, same bore centres, cranks interchange, probably a lot more but I can't be arsed to regurgitate what's posted in very good detail on the 205 forum by Sandy Brown
the 306 did not get an EW engine, nor did the 206 ever get an XU, so the xsi engines share nothing directly but the badge and similar power output.
Cam ladders are the same casting, smaller tappets other than 180 engine, same cam blanks, same bore centres, cranks interchange, probably a lot more but I can't be arsed to regurgitate what's posted in very good detail on the 205 forum by Sandy Brown

the 306 did not get an EW engine, nor did the 206 ever get an XU, so the xsi engines share nothing directly but the badge and similar power output.