I've heard that the closest thing to Ancient Yiddishkeit are the Temanim. They were relatively isolated for the longest and didn't move around much.

I'm wondering if they always had those peyos and is that also a throwback to way-back-when.

According to Haham Yoseph Qafah, the simanim (as they were called in Teman) are an ancient custom. We certainly know that at the time of the Rambam, many Jews were wearing them - if I recall correctly, the Rambam considered the wearing of simanim to be a minhag shetut (and when I speak of wearing simanim, I refer to what we're accustomed to seeing on Hassidim, not to the actual halachic practice of not destroying the pe'ah). On the other hand, and I can't quite finger where at the moment, I've also seen it written by many, including some Temanim, that the simanim were required by the Ishmaelite rulers of Arabia Felix, in order to distinguish the Jews from the Ishmaelites.

They've taken so many customs from the locals that I wonder if their way is the most authentic (not specifically the simanim).

Every Jewish community has taken several customs from their host cultures.

That myth has been debunked previously on h.com.
That said, apparently their girsa of sifrei torah are the most accurate.

theres only one difference, an aleph instead of a hei in petzuah dakah in sefer devarim.

do u have a source for your claim that rambam thought it was a stupid custom?

9 differences actually, most of them having to do with Yuds and Waws (full spelling vs Half spelling)

Yes. Many have. But what did Americans take? Hungarians? Belgians?

crocs (duh )

Most like the type endorsed by the Rambam, if that means the most accurate.

As far as the "ancientness" of Temani Judaism, that would be a more compelling myth if they weren't so Arabized and if the Rambam (12th century) didn't loom so large for them. Not that this is a bad thing, but essentially don't confuse "most like authentic Arabian peninsula culture" with "most like ancient -- and pre Arab -- Jewish culture."

by definition

Why?

If it is true that that the Rambam held that way, that may be the biggest proof that simanim precedes their connection with him. Also, it's well known that the local arabs wouldn't allow jews to shave their payos or their beards, but not because they invented the idea of jews wearing them, but rather because it had always been clear to them that a beard and peyos was part of how a Jew looked. They didn't want them to start trying to blend in, and "corrupting" their ways. The fact that assimalation was not an option in yeman, is precisely the reason they were able to hold on to so much of their mesoret. Not to say that nothing has changed since there arrival in yeman after Bayis rishon. For sure their were changes in the accent and clothing, and they "updated" their halachic system to that of the Rambam after receiving the Mishnah Torah. But those actual mitzvah oriented minhagim, that are not in accord with the rambam, are basicly excepted to from there bayis rishon roots. That is with exception to a few communities that had regular exchange with the Jews of morrroco. But there simanim were despite that, since morocan jews didn't have them.

Morrocan Jews,Iraqi Jews,Persian jews etc all had peyos, short ones tho like 2 or 3 inches and tucked behind the ear, Ben ish hai mentions that the best length for peyos is to let them grow so they hang at the start of the beard