What Rick says about the Pontiac engines' demise is a sad, but true story. Pontiac probably stayed with the block because it saved money vs designing something new. They had to keep decreasing compression to meet emission standards ... until they were running 7.6 to 1 and had 180 HP motors in the late 70s. The block and head design was essentially the same from years back. 1978 was the last year of the 400 blocks. The 455 was finished in '76 ... and the 301 came out in '80/'81 but it never really got off the ground. Pontiac engineers didn't want to go this road ... this was the dreaded CAFE standards that spelled the end of the muscle car era. I'm sure there are some people to string up, I mean, thank for that effort.
You mention why don't we engineer with that way today? We engineer engines far better today than in the 60s/70s/80s - computer design, CFD, materials science, fuel injection and tooling have all gotten engines & technologies to be far more advanced. You can squeeze 100HP or more out of Corvette motor pretty easily ... and at 505HP out of the gate, they're not exactly slacker engines. The ZR1 is a 640 HP supercharged 6.2 liter engine ...top speed of 205 MPH.
That's a production car that could probably run the 24 hours of Daytona and actually hang with most cars with a tire swap.
I hope GM gets their crap together ... I really don't want to buy a Japanese import or a, gasp, Ford, down the road.