I've actually got a Buick engine in my garage, although it's buried deep under Land Rover parts so I can't do a side-by-side comparison of the two. I've often described that engine to people as "the small-block Chevy of the UK". However, it seemed appropriate to use the small-block Chevy of the US for my build 
What makes the LS so compelling to me is not the size of the fundamental block, but how well everything else is packaged. The intake manifold is low. The coils are attached to the valve covers so there's no goofy distributor sticking out and getting in the way. Everything's just tucked into a dense 2'x2'x2' cube of horsepower. The fact that it (can be) all-aluminum is an extra bonus. It was my first look at the bare engine that convinced me to abandon my previous plans with this car. Power? Yeah, it makes a bit.
I doubt I'm paving the way for a legion of B enthusiasts to follow in my footsteps, as I'm going far beyond the minimum necessary.
As for older cars being lighter - the original car was about on par with the weight of a later Miata. But apparently much of that weight came from the engine and suspension (leaf springs are heavy!), not the chassis.
