What are the specs on the L78? And can anybody tell me anything about the 406?

The L78 was available mid-year '67 through early 1970. It was a 396, 375 horsepower, 415 lbs.-ft. torque. Solid lifter camshaft, Big rectangular port closed chamber heads, hi-rise aluminum intake with Holley 780 CFM carb. 4-bolt mains, steel crank, dimpled 3/8" rods, forged 11.0:1 pistons.
The only 406 I can tell you about is if you take a 400 small-block .030" oversize bore. Supposedly, these things make about as much torque as a 396, but weigh 140 pounds less.
I prefer the Mark IV engines, myself.