In 1987 the Danish electronics magazine “Populær Elektronik” had two articles with instructions on how to build a C64/128 interface for use with e.g. LEGO. In many ways, it’s a competitor to LEGO’s Interface A. At least one more article was planned but apparently never released.

I have scanned the two articles that you can download (in Danish) from here (PDF, 12 MB).

You ought be able to make a decent translation e.g. by taking screenshots and pasting them directly into Google Translate Images.