According to page 448 of Sutherland and Wilson's BOOK OF COLT FIREARMS these were special order items for Gil Hebard Guns of Knoxville IL made 1964-1970, with serial numbers beginning 00100 and (including gaps) ending 01164, with .38 Special guns having an H suffix. (Apparently there was a .45ACP Kit, with an 0 suffix)
Sutherland states they are basically a .38 AMU, that the original guns were supplied _without_ sights, but with the slide dovetailed, and that "grips and hammer are shipped mounted on the frame, but the barrel, bushing, and other major paarts of the kit are supplied disassembled and packaged separately."
Gil Hebard is a nationally known target shooter whose business caters to bullseye shooters--I bought guns from him in the '70s. As far as I know he's still in business. I'd suggest contacting him and seeing what information he has to offer.