From Haynes manual.....
VALVES:
1.3 and 1.4cvh:-
inlet valve opens ... ... 13*btdc
inlet valve closes ... ... 28*abdc
exhaust valve opens ... 30*bbdc
exhaust valve closes ... 15*atdc
Valve lift:
inlet ... ... 9.56mm
exhaust ... 9.52mm
Valve spring free length:
47.2mm

1.6cvh and XR but not RS:-
inlet valve opens ... ... 8*btdc
inlet valve closes ... ... 36*abdc
exhaust valve opens ... 34*bbdc
exhaust valve closes ... 6*atdc
Valve lift:
inlet ... ... 10.09mm
exhaust ... 10.06mm
Valve spring free length:
47.2mm

The XR head was revised with three angle valve seats, slightly better flowing ports, and a better shape combustion chamber with pistons to match, and different carb, thus the power hike, but the camshaft was the same as the other 1.6's.
The shafts are all interchangeable prividing you have enough clearance on the pistons and valves, but you cannot put a 1.8 one in; like trying to push a pound of cheese through your letterbox, it wont fit; different kettle a fish camshaft, and a different shaped head and pistons to go with it.
The RS1600 i dont have data for, it could be different as it was designed to rev a bit more, with less valve bounce, due to solid cam followers. Can someone confirm the camshaft data for this?
RST camshaft will be cast like the others (ignoring the 1.8) and will fit but the cam lobes are positioned for forced induction and i dont have the data for that either, sorry. More citation needed.