[IanH]

The adjustment on the GA is by shims, there is no hydraulic lifter.
Just remove the valve cover and measure the gap between the back of the lobe and the shim.
follow the FSM procedure. Gaps are specified hot or cold (sometimes both)

 

[IanH]

I know there are many cars here 200K + miles.
Yes the valves can go out of adjustment.
The older Jaguar DOHC set up specifies adjusting every 60,000 miles but newer Import cars do not recommend an adjustment interval.
So just check them, shouldn't take long, its adjusting them thats a pain.
Oh BTW I think you are right, that buying a low millage engine is the way to go, the parts are too expensive to rebuild these import engines.