looking to purchase a vintage IWC watch... is this a fake movement or not

I want to purchase a daily good quailty watch and narrowed down to
omega Seamaster/De ville automatic with cal 5xx or 6xx movement and
IWC vintage with cal 85x movement.

First of all, are there any fake movement out there with exact engraving with cal number on the actual movement??

If not, then i guess any pictures showing the actual movement can be considered as legit movement.

The attached picture is the actual movment inside the wrist watch i am looking at, is this legit ? since I cannot locate Cal number...( or I don't have an answer for the question above)...

maybe this is not even cal 85x movement.. anyway.. but is this still legit?
(cal 37521 movement?)

The movement is not cal. 85xx.

To me, it looks like the movement is ETA 2892-A2 based IWC 37521 and the watch is likely to be an IWC Portofino 35131.

A Portofino 35131 is a perfectly nice watch as such, but it is important to understand exactly what You are buying.

you are exactly right.
Now, I would like to know your honest opinion of comparison between cal 8xx and cal 37521 movement.

which one is considered as a better movement if there is, and which one (assuming same condition) would cost less overhaul cost?

Thanks

Most enthusiasts probably feel that a cal 85xx is a more interesting and desirable movement than an ETA 2892-A2. Cal 85xx is an IWC in-house developed movement with a classic IWC Pellaton winding mechanism. It has been out of production for years, so it is, if not exactly rare, at least nowhere near as ubiquitous as the 2892.

On the other hand, when it comes to sheer accuracy and robustness, it is difficult to beat a carefully adjusted ETA 2892. Because it is so common, there are also lots of good watchmakers who have experience in servicing it.

Which one is better? I think the answer is subjective, depending on how much value one puts on collectability vs sheer practicality. My heart says 85xx, my head says 2892.

Thanks again for your thorough comment.
I am looking for more reliable daily watch and easy to manage including routine service. Thus, i am leaning toward cal 37531 or eta movement as it can be fixed relatively much easier than older cal 85x movement....
I will see what i can get and it seems i wont be disapoointed with either one anyway.