Now, to the variants. You counted kai in v.10, and ten in v.13.
The kai is not in any actual ms of value; TR used it, and that's not an ms but a critical edition. So including it won't wash with the scholars.
The ten is in the first Aleph but only a few others. To include it stresses the type of authority given, as SEPARATE, so that's a doctrinal difference. It's more tenable, but scholars could easily dispute it, since it's in so few other manuscripts.
The bigger reason to exclude it, is grammar and context of prohibited oneness. Granville Sharp rule has one article covering more than one item to prove the two are related, so power and authority really are not separated: so no ten should be there, as lack of separation of power/authority is the problem stressed. The illegal unity is already indicated by the ten fronting dunamin. Same idea as pastor-teacher, no second article means it's all the same person/thing. So should be ten dunamin kai exousian to show all-in-one, which is the abomination being warned against.
BTW, that's what felled Rome: Augustus was all in one, no succession plan, and therefore the only succession that resulted was the army.
if we leave out kai in v.10, change sophia back to its classical three syllables which have no Hebrew counterpart so would not be susceptible to slurring, then v.9 is 449, and all the others are 1 higher till 10b, which is now one lower so still tallies to 490, tho I'm not sure it should. But for now, could leave it be.
John uses sophia a lot, it has a well-established name and Greek lit is full of it; but it's only used that once in Rev17.
As for v.13, leaving ten out, syllables from 13b through end 14 go down one. Remove elision from 15a's ἃ εἶδες because the sounds are too different, and the alliteration is intended (three a's, unholy, alphaprivative negative sound). So then 15a ends up staying 684.
There might be other changes needed, but those two would at least be needed since the mss nor grammar support including them. Variants I gave you have to be mentioned, but I didn't see one which ought to be included, on grammar grounds.
Biggest point to remember: don't force a sevening. Especially here, since frankly the sevening should only occur at the end (guessing). If it naturally occurs, then by the clause counts you can see why and where, cuz usually the writers pair clauses to have same syllable counts as a type of tagging.
Text sevens for a lot of different reasons, not merely to show spiritual growth. Here, the point is NO growth, but the Plan of God still works. So yeah, there might be a 490, 560 etc. to denote the Time Allotment, but we don't yet know if this is predicting specific future history like the Matt24-25/Eph1/Luke21/Mark 13 did. Maybe it does, in which case the meters will 'tag' those passages by sometimes having the same values. But don't force that, either. Just let the meter reveal itself as you do it first assuming no ellisions, unless you get tongue-tied without them. Then see what pattern results.
This is hard to do. It's tedious work. Had we all been raised on the meter since childhood, it would instead be fun.