Hey GRM, what would you do if you were me?

So my motors sitting all "dolled up" just waiting to be re-installed into the car. It's been awhile to see it like that again... 

So I was about to install some new motor mounts when the bottom bolt broke loose, which was good, the bad was that the mount now spun with it. The marry-go-round thing that i'm sure has frustrated us all. My immediate thought was to get a pair of vice grips, since that's pretty standard procedure, to hold the thing still and continue to loosen the bolt. Well the rubber ripped off without too much force and now it's awkward...

Scrape off remaining rubber, weld nut to top of metal part. If you don't have a welder, drill two holes toward the outer edge opposite each other and use snap ring pliers or similar to hold it.

Looks like you might be able to fit a nut splitter in there. In which case, just split the nut off.

First thing i would do is take a REALLY sturdy screwdriver or preferably a small prybar and fold up one edge on each side of the metal that remains on the top side. Then i'd grab that with really, really large channellocks which are cheap and everyone should have some (~$15 at harbor freight for huge ones). Then squeeze the crap out of that while someone else takes the nut off with a ratchet wrench. 

Or, if that doesn work just drill down the middle of the top side until you get to the point where you've drilled the top of the mount off of the stud just like drilling off the top of a rivet. 

I have a craftsman air jack hammer thing, could try to use that to get it to work. I'm not a huge fan of destroying old metal but if it needs to be done, I will.

I gave a half hearted attempt to use a prybar to bend the metal up and use vice grips from there but stopped half way because again, I don't want to ruin the old sheet-metal unnecessarily. I'll give another shot tomorrow with a properly sized one and stop if i see the "cup" flex before the plate. Hazard Freight doesn't exist here, so I pay full price for the same quality  LOL

If i can avoid welding to it i will, haven't had the best of luck welding a nut to something that requires any sort of force. I usually break the nut off and am left with a small mount of weld material.

Option I like the best is to just drill through the thing, some razors, a punch and my crap-tastic drill will go to work.

Thanks for the ideas! I'll try to update

I'd just cut the nut off with the oxy-acetylene torch but I'm assuming that if you had that ability you'd have just done that without taking the time to post.  Is there enough room to get a short recipricating saw blade in there?

So i figured out another remedy, went down there today fully expecting to have to cut/drill/whatever to remove the broken and old mount.

Turns out the broken mount shape is actually octangonal/nonagonal/"insert number of sides here" shape. There is also a hole that you can kinda see in the pics attached (bottom hole is super obvious but i used the ones on the side). I took a pair of needle nose pliars and shoved them in the hole to create a 'catch' that the mount-sides couldn't turn pass.

Hooray! Fresh new mounts for a freshly rebuilt motor!

Nice!  It've been wrenching on stuff for over 30 years and it still sometimes surpises me how stepping away from a problem for a bit makes it so much easier to solve when you come back.

I still think you need to buy an oxy-acetaline torch.  Every shop should have one.

How much should I expect for a kit?

Only company out here that I trust is KSTOOLS, everything else is usually junk.