I assume this is the icv, does it just unscrew for cleaning?
Fairly sure thats correct (its been a while since I had my ‘40)
4 bolts and be careful with the gasket.
There’s a procedure to re-set the ISCV once you have it back on the car.
Careful with the bolts - they are famous for shearing off.
From the XJ40 online book (old J-L site):
http://www.jag-lovers.org/ebooks/view.php?Vbook=xj40&Vsection=10.6
Just unscrew it. It is the same as the ones on throttle body Chevy engines.
bob