I just did this on my formerly california '78 a month ago. One side came out fine, the other did not. In my case, it was not that the bolt would not come loose, it was that it was totally stuck onto the metal sleeve inside the bushing. The entire bushing would twist a little bit, but did not want to break loose from that big bolt. I tried getting some penetrating oil up there, and finally did get it out. 6 foot cheater bar did not work. What finally made it let go was the oil (maybe) and about 15 minutes of forward/backward/forward backward with the 1/2 impact (did not have the correct socket for 3/4 inch)
Had that not worked I guess I would have spent about an hour or so snaking a hacksaw blade up there to cut the rubber away and let it spin free.
The only positive thing is that I did not have to use the home made press to release the bushing from the subframe on that side, all that work loosened it up so it just fell once the bolt was free.
If you are lucky you have a similar thing and not a frozen bolt.
good luck.

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andy t
'78 300d
'95 volvo 850, wagon
'86 300sdl - engine out, maybe I'll have it rolling by June

whole bunch o' bicycles