I really don't know, but I have just measured the height of that space for fitting NVMe heatsink in a Mac Pro 6,1.
I'd say 17mm of height, with a width of 25mm would fit the enclosure. Even a little bit more if heatsink is on two sides, because the lower side takes approx 2mm off from the total height I measured from the slot to the Mac Pro cylindrical case. Heatsink can be sometihng like 85mm long at the most, but depends how it's attached to theSSD drive. Uhh, it's so hard to explain with words, you know what I mean. It was too hard to take pictures with all the rulers and stuff with just two hands.
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I would make sure you get the right thermal pads with the drive (Sabrent 8TB here) if you decide to go for that one. Is it flat design, or is there a controller with more or less height than what the memory chips are? You might need some extra thermal pads maybe.
I just ordered a few EKWB heat sinks for my single sided Kingstons and Samsungs (would not fit for your big Sabrent though).
EKWB EK-M.2 NVMe Heatsink, Black
Don't mind the dimensions on that Amazon page, they are annonced just wrong in the page I believe.
In my opinion a slight problem with 6,1 is that there is no air flow directed through that SSD location. Yes, it's open from the bottom, but the top fan (and only fan in it) doesn't seem to suck any air through that route. At least it seems so to me. The fan assembly does have a round sleeve up in there on the outmost circle of it, thus blocking the suction of air from the outer sides of the GPUs.
Maybe the heatsinks will help with that a little, we can hope.