Master One

Most likely it will be the dtb that is the issue.

Yes it is possible.  The dtb is the mapping of all the hardware to the software (not just the cpu).  So a dtb that isn't a perfect fit for the cpu may work overall better for the rest of the hardware on the board.  For amlogic cpus the differences between the s905x2 and s905x3 series are not major, so a dtb for an x2 board may work as good or better for your x3 based board.  So I would look at the meson-g12a-*.dtb files as well.

As long as you understand the limitations that dante6913 mentioned, and as long as you are only expecting to use it for server work, and I would add one additional item that you should only be expecting to use wired ethernet (wifi/bluetooth support is very spotty).
I would recommend just trying the last build that supports amlogic cpus (The 5.9.0 October 14th 2020 build) and follow the instructions in the first post of this thread:
Try the various dtbs for s905x3, sm1 (or s905x2, g12a) and see if any of them work well enough for your needs.  I have a TX3x3 box which contains a s905x3 and I use the meson-sm1-sei610.dtb for that box. 
 
The one thing specific to the s905x3 that might be unclear from the instructions on that post is that you will need to copy the u-boot-s905x2-s922 file to u-boot.ext as there is no x3 specific version, but the x2 version should work (at least it does on my TX3x3 box).