While I decide what to do with the broken vise I have started on the the bushings in the differential.
It started out as usual wit a stuck bolt 
I had to use all my super powers to loosen it. It was so rusty that I wasn't able to knock/pull it out after it was out of the treaded section on the top of the PPF. That meant I had to losen the whole PFF from the transmission with the diff connected.
After 1 hour with a hammer and other heavy machinery the bushing had moved exactly 0 mm:
As any other pissed off n00b mechanic I went inside for a cold one and was prepared to take the whole diff to a shop the day after.
Luckily I got som excelent tips from a couple of guys at www.mx5-miata.no that it would be easier if I used a hacksaw to cut the surrounding steel shell.
I can't beleive I didn't think of that. The hacksaw actually fell off the wall while I was hammering on the bushing earlier on...

The next day I used less than ten minutes to get it out:
After persuading the guy at the return stand at Biltema that the vise I had bought was totally crap I got a new one :)
I worked ok for pressing in the new bushings. I used a hoseclamp to press the two halves togeter for easier fitting:
The rest went fine. I cleaned the sleeved bolt for the diff and used some copper grease to prevent make it a little easier for myself the next time the diff is going out ( hopefully to fit a LSD).
I really cant see how it is possbile to change the bushings without taking out the diff.