640’s virtually don’t exist in the UK, sadly. They suffered from split stocks at the tang generally. But, that’s not why of course.
1909’s are superb, esp for their tolerances and floorplate. But, these days you’ll have to break a military rifle to get the action, which is a shame. TT Proctor used them, and many, many US rifle builders did for some very fine sporters.
There are many other great mausers for custom rifles, including the DWM’s, ZG 47, VZ24 (older ones, esp the Persian ones by BRNO!), Standard Modell, etc.
The Peruvian DWM made is an intermediate and has the proper pear shaped bolt knob, wonderful action to work from. The stripper clip hump needs removal due to its size of course.