how can i tell if this Omega speedmaster is authentic?

front

inside back 1

inside back 2

outside back

inside back 3

crown

Marnie,

There are two different autoweight finish common on these 1140's, from what I can see mostly looks good.
The scratched in markings in caseback looks like a hack has been working on it, crown and pusher changed, lot of use over the years and of course if not in good working condition could be expensive to complete, I would expect this is at bargain price given condition.
One thing that does concern me a little so the auto wind section is slightly different color to main movement would need to strip and examine the watch to be sure this may have simply been a replacement part/module. its very old had lots of use so it is what it is now! main movement I think should be 2890
PS think I can see the "omega" in crystal center

How can you see that on the crystal! What would be a good price for it? Thank you.

also in photo "inside back 2"left hand side is the number 2890-2 What is the stamp above that?

I do see the mark on the crystal

The stamp will read ETA, is the watch running, all chrono function working correctly, pushers tight, I see them for sale nice examples $1000 to $2000, this I would say is a watch to use and enjoy once serviced and repaired, given condition would be hard to sell as many other better examples out there.

Hi. That looks to me like an 1140, not 1040, and for sure is a Speedmaster Reduced. Thanks, Nick

Dial, hands and bezel look correct and the case doesn't look over polished. The crown and pushers are okay, maybe replacements as Chris says, but they look correct.

In good running order, new crystal, probably around $1500 judging by recent sales on the big auction site. A little hard to tell--most of these have the black dial.

wow did I make a typo, yes 1140,
Given the replaced pusher, crown, questionable auto-weight, sticking pushers, extensive service required, no Omega metal band, you would be ill-advised to pay more than $600 for this in current condition.

A quick look shows for $1500ish a far better examples sold, there is one looks new with box and papers two tone band $2k