Use a jack and a block of wood to gently lift up on the engine at each mount location, if it moves much or is broken free replace the mounts.
Use same jack method to support engine while replacing mounts, it's that simple.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-