The system should work as before, since we are cloning it, basically. Just using a very aggressive disk imager to do the raw copy. One that is more persistent than most others. If you have an older version of office installed, that older version will be there.
As for replacement... I assume you mean the office suite and not the HDD... In which case, your options are limited. Microsoft likes to change the file format every version of office they release as one of the ways they do lock-in, meaning any free alternative you may choose will be constantly playing catch up, and clients sending you Office formatted data will likely not take the time to use an older, compatible format with the save-as dialog. This means they will be sending you files with the "latest and greatest" format that the free alternatives to MS office will not know how to open, leading to much wailing and gnashing of teeth if your clients do not follow your instructions and fail to send you back-compatible files.
Naturally, Microsoft does NOT see this as an abusive monopolistic practice that leverages their market dominant position to discourage the use of alternatives. Of course not. /s.
That said, the free alternative list includes but is not limited to:
Libre Office (When Oracle allowed forking of Open Office after acquiring SUN microsystems' IP, the community salvaged the project under Apache licensing, under the libre office name. It does not have the bullshit Java dependencies that OpenOffice.Org has, has some unique improvements after having been forked, etc, but is still based on OO.org)
OpenOffice.Org (descendent of StarOffice, owned by Oracle. oracle is even more abusive than Microsoft and treats their customers like toilet paper. Suggest avoiding and using libre office instead.)
Both have an excel clone called "math", which can open and edit older excel files, but is not feature complete, because of MS's evil attack lawyers concerning look and feel, trade dress, software patents, and all that jazz.
If you mean replacing the whole system... That is a bit overkill, especially if the old hardware is working, side from an aging disk drive, and if the plan is to milk the system until if is a withered corpse to get max return on the investment.
In general, if the system has a " legacy boot" capable uefi firmware installed, it can be coaxed into running windows 7, as long as you can find USB and SATA drivers.
In general, windows systems have been capable of running multiple monitors since windows 98.
Sadly, unless you want to bend over for the rough anal violation of windows 10's metrics and tracking that you cannot actually disable despite the screams of the fanbois to the contrary, you will end up forced off the windows platform as win7 is end of life. The only real way to reign in win10 is to aggressively firewall it to keep it from contacting the mother ship, and aggressively monitoring it after every update to see if MS has found a way around your cockblocking.
I made the switch to Linux quite some time ago for this very reason. WINE may not be perfect, but it can run a surprising amount of windows software, including older versions of MS Office. There is better compatibility if you don't mind shelling out a few bucks for codeweaver's non free fork, crossover. Mint feels a lot like win7, but is still Linux.
At this point the only real thing MS understands is a mass exodus from their ecosystem. This is exactly what they are trying to prevent with the like of Office365, by locking you into software service hell. The idea that they should accommodate users, and not themselves, appears incapable of being understood by them. Like any abusive relationship, you should seek other options. That's what I did.
My gaming rig upstairs runs win7, and does just fine.
For actual work, I picked up a cheap Chromebook, hacked the bios on it with MrChromebox, then installed GalliumOS. (An Ubuntu based distro made specifically for Chromebooks.). I have come up with a workable solution to having to use an SD card as /home, where I use tmpfs mounts in /etc/fstab to prevent excessive writes from things like the browser cache from nuking the card. Works just fine for basic office tasks, and uses local storage. Minor annoyance at bootup since I have to use the legacy boot package on my system, and so have to use a magic button combo on boot all the time. There is a solution to that, but requires taking the thing apart to remove a write protect screw, and I will just deal with the petty annoyance. I use libre office on said hacked Chromebook.
Probably not the answers you really wanted, but MS is not going to stop herding you like a lamb to the slaughter toward their goal of milking you eternally with software as a service.