Well that was unexpected! You don't even have a car motor
729/1 was a late '50s 1600cc intended for inboard motor boats. Very funny! It will have an A crank, early rods, small oil pump, low compression, mild cam. Now I'm puzzled how it was adapted to a 912 and the rear motor mount bar. Look around the front cover carefully. The serial number may be there, but in a different place than usual.