As I see it, there are a couple of issues.
First is the (structural) oil pan. The Miata transmission has 4 oil pan bolt holes, a wide spaced pair near the top of the oil pan and a narrow spaced pair near the bottom of the oil pan. The 75mm pans have mounting holes for the widely spaced upper pair, and allow you to shave the bellhousing flange into the unused narrow spaced lower pair. However, the Ranger transmission only has 3 bolt holes into the oil pan. The drivers side near the top of the oil pan and the narrow spaced pair near the bottom of the pan. This means that you'll only be bolting into the oil oil pan on one side, which is certainly not what I'd call structurally efficient. If I'm not mistaken, here's where the block/pan interface would be:
Attachment:
IMG_20230317_233455849.jpg
Second is that I don't see where you're going to get any benefit from the shortened pan anyway. As far as I can tell, it's going to be sitting well above the bottom of the chassis. Here is a side shot of the transmission as level as I could get it, assuming the ribs on the sides of the case are reasonably parallel to the internals. Consider the unmodified bellhousing flange as flush with the bottom of the chassis.
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IMG_20230317_233735116.jpg
With a 1" tube shown for reference, you'll see that the 'annoying' drain sump still has ~1/2" of clearance to the bottom of the chassis.
Attachment:
IMG_20230317_233929594.jpg
Now you may be thinking that if you take 1" off the bellhousing flange and bring it to level, that means your drain sump would be protruding from the bottom of the chassis by another ~1/2". However, that would only hold true if you also eliminate a critical tube in any Locost frame I've ever seen. Otherwise you find yourself with a mere ~1/4" clearance between the frame tube and the 'high' point under the transmission.
Attachment:
IMG_20230317_234008462.jpg
So even if you were so confident in rigidly mounting the engine that you were willing to bring the whole transmission the rest of the way down until it effectively rests on the frame tube, the drain sump would still be above the bottom of the chassis, and the bellhousing wouldn't actually be hanging down far enough to even worry about. The 75mm oil pan would actually be sitting notably above the bottom of the car... And that's assuming you don't run any kind of triangulation under the transmission, which would push it all even higher.