I am putting a 39 desoto overdrive trans in a 37 dodge coupe. This OD trans has a solenoid ,but does not have a rail lockout switch or a governor(no provision for either). How does this trans sense engagement speed? I have manuals for the non electric B-W OD and the fully electric B-W OD for 1940 and up, but the 39 B-W OD seems to be the cross over year and I can find no info at all. Any help will be appreciated.