Do you have a second bolt hole somewhere on the hardware of your dogbone mounts? My friends Impala with the L36 actually had another bolt hole you could slip a bolt through to hold the engine in the rotated position. With his all we had to do was pulled it forward a little by hand, because it basically just flopped forward....Im not sure if he had a bad mount somewhere or what.
The setup may be different between L36 and L67, and may even vary between models, I dont really know. My 3.5 only has one dogbone mount, and nothing to hold the engine in place.
But a tie-strap, or come along will work just fine. The Chiltons shows them using a small turnbuckle.
2000 Oldsmobile Intrigue 3.5L DOHC V6 15x,xxx miles "The Forgotten W-Body"
shaved badges, Eclipse HU, Pioneer TS-A1370R'*, Pioneer TS-A6971R'*, 20% tint, cleared corners, Silverstar Hi'*, 9005 Low'*
Fenderwell Intake, Hi-Flow Cat, U-bend delete, GMPP Handling Kit, MOOG endlinks, and 12-inch front rotors
1996 Bonneville SE RIP 157,751 miles, totaled 8/29/05