Is an offered Montblanc 144 Solitaire Silver grain from the 70s genuine if the clip carries no serial number and no PIX, only 'Germany', and the 925 hallmark sits at the top instead of the bottom of the cap?

The features described are completely normal for a 144 Solitaire of the 70s and speak for an original. Serial number and PIX engraving on the clip were only introduced later; older Meisterstücks bore only the '925' hallmark at the top of the cap and had a fully gold nib without platinum inlay. Comparison pictures can be found on fountainpen.de. A price around 250 euros counts as defensible in good general condition; before purchase the nib should be tested in writing, since repairs via Montblanc service can become expensive.