Yes, short of a seriously worked crossflow six, these engines are the "small" sixes to beat. Cheap as chips with a 2-barrel Carter and headers, too.
A friend races a 245 w/45s in a '70 Valiant sedan body. He has his own flowbench, does most of his own stuff. Reckons he's cracked 300 horses (fly), but aiming for 400, N/A. Only mods are a deep oil pan, surge tank/electric fuel pump, electric water pump.
Haven't heard about the Buick, do you know where it's been raced?
Cheers, Adam.