Rear Suspension impossible to remove

I had my celica at the garage yesterday to get a set of coilovers fitted to the car, he had no problems fitting the front ones, however when it came to the back he couldn't remove it as one bolt was rusted stuck as he said, now he tried hitting it very hard and even tried heating to remove with no avail.

His next choice was to cut it off and then just replace however that meant my car would be in the garage for a few days and i need to it to travel back and forth work so i asked the guy if i could take the car home as it is now and buy the part that he was gunna cut then bring it back to get the back coilovers fitted and he said that wouldnt be a problem.

Now i kinda need help on finding what the part is called or what the part number is so i can order it either online or through my local toyota garage.

Here is a (not so good) picture of the bolt.

Linked Image

now im just wondering is there gunna be any other problems with replacing this rear suspension, that i should be prepared about?