Removing Motor Mounts 1974 C10

[Cadillac Kid]

Hello everyone.

I am cleaning up my engine and engine bay and I bought motor mounts and thought I should change them. I removed the through bolts from the mounts and then jacked up the motor. I pulled two of the three bolts out of the bracket that is attached directly to the block. I was not able to get access to the third one. Then I started realizing that there is no way to remove the mount from the bracket that is attached from the frame because you can't get a wrench to hold the head of the bolt from spinning on the bottom side. Do you have to pull the entire bracket that is attached to the frame off in order to change just the motor mounts? How do you change these motor mounts?

Thank you

-Gavin