Is the entire running gear 57- - - -engine, trans, and bellhousing, or has the 57 engine been grafted to a 1940 bellhousing and trans? That's important, as a different starter and flywheel was used for the 12 volt electrical system beginning in 1955. A 6 volt starter and a 12 volt flywheel do not play well together. There is a different number of flywheel ring gear teeth involved, and the pitch and root circle on the starter pinion gear teeth differs from the 12 volt, although both of them have nine teeth. Even if "It worked when I parked it", it might not have been right. a 6V/12V mismatch is noisy, and the gear teeth wear quickly.
Jerry
