The Zasty 9.3's are not opened up any more than other standard calibres. They are opened up along the lines of an FN commercial - the shortest box they did, was nominally 86mm long (they vary a bit). The 1909 box is shorter by about 2mm at the front.

I've seen a lot of 1909 boxes fitted to actions which should have an "86"mm box. You can see an air gap between the top of the front mag wall and the feed ramp. I've been hauled up on this, because it is possible to squeeze many factory 9.3mm crackers in the short box. However, Paul Mauser used the longer box, and for good reason. Also, with the short box wall hanging in mid air, there is a much compromised juncture at the feed ramp. I'd reckon if he were alive, Mauser would see it his duty to give those guilty of such, a proper good birching (haha).

Widths at the front and rear are another story, I would have to look it up or do the maths. Width at rear would be fine but at front, perhaps a beesdick tight - that being another issue entirely (that can be overcome). Pushing the front wall out, with a std floorplate you don't have much room the way the front wall shoulders are machined. Some actions, it won't work. It's possible to weld and re-form that shoulder and make it look right with a new (normally straddle) floorplate. That is only cosmetic; down that low you only need to accomodate the spring and follower of course.

Custom bottom metal is getting hard to get nowadays locally. Another option is getting a cheap but very well made FN .30-06 military box in good shape, reshaping the trigger guard and doing a hinged floorplate conversion. Hell, look at most Rigby .275's.......they often used this style of bottom metal (in an appropriate box configurtion).