For printing I recommend strong paper with a weight of at least 160g/qm (Gramm per square meter).
To print the sheets in original size, you need to check the dpi (dots per inch) setting and adjust it if necessary. (This specification is irrelevant for screens, but it influences the quality or size when printing.)
The standard sheets (at about 26 x 17.2 cm) are slightly smaller than A4 or Letter size. (The posters at 25 cm are usually a little shorter.) In the page preview of your graphics program, it should appear about like this:
Note: I have noticed that the dpi information in the older files unfortunately can be incorrect sometimes. Especially with the sheets from the 80s. This problem will gradually disappear with the progress of new scans in 300 dpi.