Hi James,
My fintail has the early remote booster which is entirely different. It seems that the original pagoda boosters have a notch out at the top rim of the booster directly above the master cylinder. This is the easiest way to identify it quickly. Also pay attention to the attachment of the engine vacuum line one style screws on and the other style has a plastic fitting and the vacuum hose slides on and is clamped. I have seen the later finback booster used and boosters from the W114 and W108, W109 series sedans used. As long as original boosters are available or re-buildable I would suspect that you would want to stay original. In a pinch you can substitute possibly.