There were two different Ace models in addition to the conversion unit.
The first, original ACE, was made 1936-1941, with a few assembled around 1947 from parts. About 11,000 were made. The frame has only the serial number and the Colt VP with no other markings. It uses a Gov't Model frame without an ejector, and a special smaller and lighter slide and recoil spring. It does not use a floating chamber.
The second, the Service Model Ace, uses a standard Gov't Model frame, and a normal size slide. It has the floating chamber which increases felt recoil to give a feeling more like that of the .45. It was made in about the same time period, 1935-1945; about 13,000 were made. The serial numbers begin with "SM".
The Conversion Kits have been made since the late 30s and usually kept up with the latest style of slide used for the civilian Gov't Model. They are still made. The conversion units use the floating chamber.
Jim