How to remove caps on cylinder head

[nimbus]

Hi!

I'm wondering if anyone ever tried to pick a large allen-key and remove the two caps in front of the cylinder head on a NORD engine.
Reason for asking is, that my car, by some previous owner, was equipped
with either airconditioner, oil-cooler or something of that kind.
The two caps has therefore been modified with a threaded stud sticking out.

I would like to remove these and replace with standard caps.
By the way - what do you call these caps? - is this the correct name for them or?
Anyway I'm not able to remove them with an allen-key because the
threaded stud is mounted there - so I need to go for the solution with two
nuts meeting each other counter on the thread and try to remove with a wrench.
But the caps seems to be stuck really bad, and I don't really dare to use force.
Does someone know if those caps normally sits tight, but will eventually
come off.
It's not the most common thing to unscrew on an Alfa as they never need
come off.
Alloy is fragile and I'm afraid to harm the thread in the cylinder head.

Hard question to answer maybe - hopefully anyone has some good advice.

Picture below should explain what I mean - my engine on the right

Thanks!

[Andrew]

Get the proper size allen wrench, or failing that, get a bolt with that size head and turn the bolt with vise grips or something. I've seen them removed with a pipe wrench, which is not the best way to go.

Andrew