great job bug!!
i bet the air was blue!!!

 

I soaked the studs in wd40 for a week, removed the rad for better access and 'cracked' the stud nuts one at a time.
Two studs snapped straight away but at the nut point some studs came out whilst the nuts came off others.
Extracted one stud but the last one, far right lower when looking from front, refused to budge. Rather than snap the stud in the head I ground a few mm of the collar which gave me enough to put a new bolt on.
The nuts are 7mm thread and soft so don't force them. The torque setting is pretty low.
All done but used 2 cans of WD40, 2 stud nuts as I stripped the thread on one, and 2 new studs due to rust/thread damage, substantial sweat and tears.

 

Well done mate! B4stard of a job!!!

Mine turned into an epic tale of woe all because of a snapped collector box bracket.

Why the **** do they make the studs so soft?

Replaced all of my studs/nuts with stainless steel, hope never to have to do it again, but if I do, hopefully they'll come right off.