The 454 LS6s are the rarest Chevelles out there. They were only made in 1970 and Chevy only produced 20 of them A person could get a RPOz25 which came with a 402 cubic inch engine or a RPOz15 which came with a 440 cubic inch engine. The LS6 was an upgrade that was only available on RPO215s. The LS6 upgrade added 100 horsepower to the RPOz15, allowing it to produce a total of 560 HP. And upgrade cost an additional $263.30
What is known for sure, unlike exact power numbers, is that the LS6 option brought with it a 4.25-inch bore and a 4.0-inch stroke (same as the LS5 engine), solid valve lifters, a high-performance camshaft, 4-barrel carburetor