SBC's and BBC's aren't going anywhere, LSx's are just another option. Depending on what needs to be done to a car it may be logical to stick with the SBC's or BBC's but in other cases it might be reasonable to go with a LSx. It also depends on budget and personal taste. Someday (when I have more money
) I will get a LSx for my '56, but that is what I like and it makes sense because I have to have to fix/change things that the previous owner and time had done to the car anyway (motor mounts, radiator, gas tank, etc).
David