Retrieving Data from Sled. Doesn't Fit?

Those four "posts" should be the mount posts that secure the hard drive in position inside the MacBook Pro chassis.
They can be unscrewed with a torx T6 driver.
If you need more help, check this guide for replacing the hard drive in a 2012 MBPro. Step 9 should show you the little culprits. iFixit will even sell you the correct tool, if you can't find one...

 

I assume that by "sled", you mean a drive enclosure (where the drive can be installed in an external case) --- or a dock (where you just drop the drive in place, usually vertically) (?)
Anyway, the connections on the hard drive will be standard SATA, and the drive would be a standard 2.5-inch (laptop size). Any enclosure sold for that purpose would be of a standard size, and would accept any 2.5-inch SATA drive.
The little posts make the drive too wide. Remove those posts, and you should be fine.
(also assuming that the liquid spill did not spread to the hard drive electronics board. I have seen that happen, where the drive was also damaged. Hopefully, you won't have to deal with that !

 

The screws shouldn't be tight, if you have a mini flat-head you should be able to undo them (If necessary). They're only for securing, so 2 is all that's needed when you put it back in unless it had plastic clips holding it.

 

You can try small tools, like a jeweler's screwdriver (the size for eyeglasses, etc.)
Or, a small crosspoint (Phillips) screwdriver --- looking for some tool that will reasonably fit in the screw head, and fit good enough to allow you to loosen and remove the post. A small allen key may do the trick, as I expect you don't care if the screw is somewhat stripped, as long as you can remove it. You can test a few different sizes, and see if you have something the is close enough to the right size. (Or be good to your hardware and find the right tool the first time --- it's a T6. The sets that give you torx drivers will usually have that size.

The drive will almost always have all 4 side-posts in place, as the hard drive is not secured with the side-posts. They fit into bosses that are designed to hold the posts, and one side has a bracket that screws in place to hold the hard drive in position in the chassis. That bracket has its own screws (2), and must be what New_Mac_Smell was thinking about.
And, it's likely that a small flat-head screwdriver will fit, but it needs to be pretty small.