Thanks - I don't think that Google Books link is relevant, it does turn up the word "DELCO", but nothing related to tools, I think it finds DE1 because the OCR of the text can substitute a "1" for an "l". I have had suggestions that it is for fuel injection, starter is a good guess also - the fact that it says "for DELCO" suggests that it might have been in a kit with wrenches for other brands of whatever the kit was intended to work on.
Does the small end also come close to matching a Wentworth size?