It is not so easy, anymore to get one of the original wolf/coyote fur-trimmed hoods; the later hoods come with some awful white synthetic crap.  The M-1951 parka hood can also be attached to the same-era field jacket; that's what the button holes on the back of the collar were for.

The reason it's called a fishtail parka is because when seen from the rear, the bottom hem had a sort of inverted "V" look.  Reason for this is that both sides of the bottom hem had drawstrings, and could be tied (seperately, of course) around the user's legs, giving added protection from blowing snow.

The early wool liners were toasty warm, but were soon replaced by the so-called "frieze" liners, which were a bit lighter, but not so toasty.  The much later fiberfill liners will also fit, but are the least warm of the lot.  Field jacket liners can be made to fit, if need be, just make sure the liner is the right size for the fishtail.

All things considered, my advice to to find something a bit more modern that is well-made, and suits your budget.

You're right; it's an obsolete design.  Most anyone except a collector––who would not wear it–– would be better off with a good gote-tex shell and some polypro/fleece underlayers.

A few thoughts about the button-on hood.

The originals had real animal fur, the later ones some white synthetic.  The reason for the fur was because when the fur was new and still had some of the animal's fur oils on it, it would resist the freezing of the user's exhaled breath.  In addition, the fur more-or-less blocked the ingress of snow and so forth onto the user's face.  The older mil hood––and maybe the modern version–– had a soft wire inserted along the entire forward rim of the hood, right alongside the seam between the fur ruff and the cloth to which it was attached.  This was a very good feature, because the user could easily tailor the opening of the hood to obtain the max amount of visibility and also face protection.  A lot of high-end hoods lack this feature, and that is too bad.

As a rule, the newer parkas and hoods were of nylon/cotton fabric, and had the more modern style OD buttons, seen on modern Woodland camo clothing.  The older units were made from mostly (or even all) cotton), and had brown buttons similar to WW II style units,  the older hood was also lined with real  wool, as opposed to the poly/cotton thin fleece of its' newer version.

No version of the parka has any innate water-resistance.  The garment was intended for very cold environments, and water resistance was a spray-on application.  Laundering will remove same, so if you get, or have a fishtail, plan on applying some spray DWR to it.

Looking at the fishtail parka's evolution, IMHO the original varsions were superior in warmth and user comfort/protection.  The later versions nylon-cotton fabric might have an edge in durability generally speaking, but was susceptible to excessive damage/melting if exposed to the sparks from a camp fire.

Such a "dumbing-down" or even "costing-down" is very common with US mil gear now, and has been over decades.

I could give many examples, but be advised that the latest piece of kit––speaking of field gear only, not high-tech items like NV and such–– may be inferior in some ways to the original version.  It will have what the majority of users want, made in the most cost-effective way possible.  The newest items may lack some features that the minority of users found useful, both for lack of demand, and for cost-savings.