Outside of the "timestamps" of "soon", are there any indicators in the book of Revelation that its past history? I think the best argument for your view would be not the "soon" statements but the "Five have fallen, one is... one is yet to come" etc. of John. Because a man's lifespan is only so long, which means the 8th king must of happened in the first or second century.
Btw: What about Revelation 20? Are you amillennialist or premillennialist or panmilennialist?
There are so many things to consider, I think the understanding of "age" ''latter times" end of the age" .. this is so powerful once you understand what was being spoken of in the OT and NT.
I think the time stamps is how the "dipsey" indoctrination first began to fall off my eyes, they are undeniable and audience relevance changes everything.
How people expressed concepts back then is also another thing I had to come to understand ... for example 1,000 as used in the original language should be interpreted qualitatively NOT quantitatively.
I think if you look into the history "the five have fallen and one is yet to come" can be also understood... so yes first century.
As well the Book of Revelation was written before 70 AD there is plenty of good information to support this now.