identify the XS engine

[Richie-Van-GTi 72 2 Cars]

My daughter bought a little project car which apparently has the XS engine in it (its a 1.1 Trio with conversion), The engine runs really well so i want to video it and get it sold, she has a full 1.9 package to go into it. How can I confirm that it is the XS engine? Its an alloy block with carb. I cannot see an identification tag anywhere obvious.

 

[calvinhorse 870]

It will have 3S cast onto the front of the head