Story identification: Make your own human kit (short story, circa 1950's)

Question

There is a short story circa 1950's with the following plot: the main hero (young men) gets (maybe via a post) a kind of do-it-yourself kit that allows one to create various life-forms including human. He starts with simple life-forms then tries to create more difficult ones. Finally he decides to use the kit to create a copy of a girl who he loves (she doesn't love him). To prepare better, he decides to create first his own copy. When he creates a copy, an officer appear and explains that the kit was delivered by mistake and it belongs to a different time. So he decides to get back the kit and kill a copy. However, the copy claims that it is the original and the officer believe the copy, thus killing the original hero.

I read it about 15 years ago in Russian translation (I believe it's a short story by American author), most probably in a series of other short stories. However, now I wasn't able to find this story using search engines neither in Russian nor in English.

Answer 1

As per "Short story about mis-delivered cloning kit from the future,?", this is William Tenn's "Child's Play". This review neatly summarizes it, as excerpted below, but the only difference from your description is that it only works for building humans.

He will learn the box contains something called "Bild-A-Man Set #3... intended solely for the use of children between the ages of eleven & thirteen... will enable the child of this age group to build & assemble complete adult humans in perfect working order".

As per your description, he does plan to build his girlfriend, Tina, who was going to marry another man, but tests the process by building himself. And indeed, the officer who arrives destroys the duplicate instead.

Things will come to an abrupt end when he dups himself, so he can sort out any human-making problems before duplicating Tina. Only the dup got vitalized with all of Sam's thoughts - including the though to disassemble the dup!

Confrontation, intervention from source whose package was misdelivered, & horrific ending. Census Keeper, a manufactured being from future sent here to fix the delivery error, misjudges the real & dup, & ends up disasssembling the real Sam... so dup will live!

Ilya accepted that this was the correct answer in the comments above, and attempted to mark it as a Duplicate of the above. This was reversed as the other answer was not accepted.

@EikePierstorff, you are right! I'll mark my question as a duplicate then. Thanks a lot! – Ilya V. Schurov Jun 9 '16 at 18:34