I don't know the exact weights of the motor, I do know its approx 115 lbs heavier than an 2.5L 4 Cylinder, if that helps. Also, to say they're all buick blocks are niave. Its just a production motor that GM designed to run in different lines of their vehicles. Newer ones are run in (to name a few):
Monte Carlos
Park Avenue
Grand Prix
Regal
Try looking at
www.l67swap.com . They're forums have some decent information. I can do a measurement on my L67 that I have, and let you know. What were you curious about?