Bad acceleration, bad gas mileage, low vacuum; could be camshaft timing is off. If that has been confirmed as correct, then you can be pretty certain that bad compression rings are to blame for those symptoms and stuck oil rings for the blue smoke. A compression test may show false readings with leaky oil rings. A cylinder leakage test will be reliable. If the test show GOOD rings, then you have raw fuel washing oil off the walls and causing your mileage and oil problems.

Turbo engine is sort of known for cylinder and piston wear causing excess wall clearance and the noise you described...but usually only in one cylinder (#1 often). If all cylinders are bad, I'd suspect that your car was run without an air filter in a previous life.

Don't waste too much time, or any money, thinking cylinder head for anything but a misfire in one cylinder on a red engine. The bottom end is much higher on the list.