Bob,
I did this with the motor in the bike. One stud had iffy threads and would not work with the 2 nuts method.
I had to weld a nut on the stud and got it out that way.
4 new studs and seal on all threads and no more leaks. 2 years.

Baz

email (option): binnawan@iinet.net.au

Thanks for that Baz. I'll have a go soon.