The reason a second hand engine is the best bet is because the individual parts to replace new would cost more than the whole engine.

That guy didnt mean your cars body will fail with a more powerful engine... He meant that the chassis of the car wasnt made to handle a lot of extra power. People that do these things to old cars have to upgrade a lot of other parts of the car to get it all to work.

You throw in a turbo with stock suspension and see how far you get. You might even rip apart the drivetrain on a car that old.