Those, briefly, are the criteria I would apply. I am taking you at your word: this is transcription of speech. No redrafting is allowed. You can't make them singular, for example, simply because you're writing rather than speaking, even if you think that someone would say "two ninety" rather than "two nineties" referring to a model called 90 (which I don't). We have to assume that someone said "two nineties" and work out how to write it.

Well, the first thing to say is that I doubt everyone would agree on one answer, and people certainly do take different views on how to write "awkward" plurals, especially plurals of numbers written in digits (e.g., decades). There are still plenty of people, mostly in the United States, I think, who write "the 70's". However, the general (not universal) consensus is that this apostrophe should not be used expect in certain exceptional cases, which include single letters, for example: "mind your p's and q's", "his t's are difficult to read".

This raises a general criterion: the pragmatic question of readability. Use an apostrophe to form a plural if not doing so would make it difficult to understand when read. This is not true of 1970s or even plurals of initialisms (CDs), but might well be true in some cases.

The other general point I've mentioned is reflecting pronunciation. This arises in the case of the model called 90s in your list. Surely this is pronounced "ninety-ess", not "nineties", so the plural is pronounced "ninety-esses". So maybe you should write "three 90ses". But a reader might well wonder what this means: is there a model called 90ses, of which this is a zero plural, does it mean three of model 90se, or what? So here, I think, is a very good case for an apostrophe: "three 90s's". And if we're going to use one here, I think it makes sense to use one for model 90 too: "two 90's". Personally I would favour "two 90's and three 90s's".

Incidentally, italicising the model names, as you have done, might aid clarity, but that alone would not make me dispense with the apostrophe here.

As for the others, I would treat them as common nouns, but with two provisos: (a) you must reflect how they are pronounced, and (b) the model name must remain unaltered in the plural. So "Megaradiuses", not "Megaradii" (which fails on both counts) and "MegaMemorys", not "MegaMemories" (which fails on count 2: "MegaMemories" would imply that a MegaMemory" is a kind of memory, which it isn't).

Beyond this, I don't think inverted commas are needed and I wouldn't use them, single or double.

To sum up, I wouldn't use any of your options, because I wouldn't do the same with all these models. Just because you use apostrophes in the first two (if you do) doesn't mean you should use them with all. I can't see any argument, other than consistency with the first two, for using them with the last three, which are not digits. And the consistency argument wouldn't make me do so.

"So that's two 90's, three 90s's, four MaxRadiuses, five NanoGlasses, six MegaMemorys, and seven WidgetKings."

I doubt anyone will agree with all of this!

There are many discussions of the apostrophe plural, in particular, online. Here's a useful one:
https://english.stackexchange.com/questions/55970/plurals-of...

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Note added at 1 hr (2019-06-21 07:33:35 GMT)
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PS. On inverted commas. I can see the argument for considering them, but I thnk they're a bad idea; you lose more than you gain in readibility. They give the text a very cluttered appearance which takes a few moments to decipher. The problem is worse, perhaps, with single inverted commas, because they can be mistaken for apostrophes. And I'm not mad about using italic. The difference between italic and upright type is not clear enough to be readily visible, and changing from italic to upright in the same word is downright awkward to read.