Park on level ground, wheels chocked and parking brake on. Place the car in neutral. Engine off......
You can disconnect the front, upper dog bone motor mounts. Some have a hole cast in the metal arm to rock / pull the motor forward somewhat - then put the front mount bolt and nut in (to hold the motor forward). On some engines, you must disconnect and/or remove the air box and snorkel. You can put a small breaker bar in the engine side bracket for the mount, and pull the motor forward. It is easier with a helper.
Some companies make a strap or a bracket to attach to the motor mount and the core support mount, and ratchet the motor forward - or use a socket wrench to turn a nut on a turnbuckle to slowly move the engine forward.
If you do this, ensure that you are confident the engine is secure before you start working on the rear plugs. Don’t just rock the engine forward and put a block of wood between the manifold and the firewall, which could be easily knocked out (and crush you while your’e working on it).
I have used this method on a 2004 Pontiac Grand Prix GT2 (non-supercharged) with the 3.8 V-6, owned by a relative - and other FWD GM transverse V-6 models.