What arms will successfully mount on a Linn LP12??

Well, I've said it to other Linn owners, and I'll say it again: the Naim Aro unipivot tonearm. A lot of people have negative feelings about these arms (I mean unipivots in general) but in my experince they sound excellent. The Graham is a case in point, the unipivot being the most easily achieved near-perfect bearing attainable in the physical world, due to it's design, and it sounds it. That's two tonearms which sound good on the Linn, and they're both unipivots. If you cannot find a used Aro within your time frame, then consider the host of other resonably-priced (new) unipivots out there: the Bluenotes, the Audiomeca, the Kuzma, the Clearaudio Unify, the Moerch, the cheaper VPI, and so on. There must be some in this long list which will physically suit your 'table. All of these modern unipivots have clever design features as well.

Any Linn tonearm or a Naim Aro are good on an LP12.

Jeff, I can comment on your sub-question about the black Ittock LVII.
I have had one for about 7-8 years, on a Valhalla/Cirkus deck with serial number in the 51000 range, sitting on a Target wall shelf. The mat is the standard felt mat(with the special magic static that only LP12 users can see stuck onto the back sides of their LP's, , but that Linn denies is a nuisance). After trying several different cartridges, I was still not satisfied with the solidity of the bass or the impact character on drums. I wasn't looking to shake the walls -- I just wanted the drums to sound like something was whacking them directly. But basses sound distant, limp and watery, and drums sounded like a blanket was laying over them. (But everything else about the sound was fine.)
The depth of my dissatisfaction was reached after getting a new Linn cartridge fitted, and having the deck tuned up by one of the specially blessed-by-Linn super dealers in England where I was living at the time. Many bass passages were so reduced that they were nearly MIA, even on acoustic Grateful Dead numbers.
Out of curiosity, I took the LP12 armboard I had just had replaced, and mounted it with an SME Series IIIS -- admittedly one of the cheapest arms from SME days of yore. I took off the Ittok LVII and new arm board, and put on the old armboard/SME IIIS with a relatively inexpensive high-output MC from Audioquest, early 90's vintage. I ran a 1-meter Kimber PBJ out of the arm base. Bingo -- bass lines that had receded into the distance were back, and drums sounded like they were drums again -- not bone-crushing, but realistic at least. The top end was NOT as spacious-sounding or resolving, but it was still okay. I listened to this for a couple years. I should noted that this arm is not like modern hi-quality SME arms, which are heavy -- the one I used is extremely light. But I'm not really trying to say that it is a great arm for the LP12. My point is that it presented TO MY EARS a more realistic sonic picture than the black LVII. The LVII significantly bettered it in some aspects, but the LVII's shortcomings outweighed its strengths compared with the cheaper arm. And yes, I had tried the AQ cartridge on the LVII before. It sounded crummy on the LVII, and bueno on the SME.
I eventually moved up to an Ortofon MC30 Supreme, and out of curiosity again (was that LVII really as lame as I remembered it?) put it on the Ittok LVII and had it re-mounted. I had the whole thing re-tuned and sorted by another blessed-by-Linn dealer in Virginia where I am now, and the drums still sound lame, and several bass lines just kind of fade into the background with no presence at all. Dealer tells me that moving to the Lingo power supply will cure what ails me, but that's what I heard before moving to the Cirkus upgrade, and it did not happen IN MY CASE (though it supposedly has worked for others).
So I'm thinking of trying a modded RB250 or OL Encounter first, but I may just abandon the Linn ship altogether and go with a VPI. I've read from others that I'll never get satisfying bass from an LP12 regardless of upgrades, but I haven't been able to compare the VPI's to check them out either. I spent 1 hour 10 mins at a Wash-DC area dealer TRYING to do that, but after a 3-Stooges comedy of errors presented by the store staff, I finally had to leave to return to work, without having been able to hear one properly (another long story).
Short answer: I have a black LVII, and I do not see any great sonic magic about it. The anti-skating calibration markings are off as several have noted before, but this is not a problem if you just adjust by observation anyway. But it IS easy to adjust the height, however, which makes it a breeze to experiment with VTA.
In case you're wondering, I DID experiement with different pieces of both ss and tube gear and speakers in the chain, both at my house and a friend's. Results were repeatable and uniform. I think the LVII must do something great for SOME people's ears, but it just doesn't do it for mine.
--Brett

the rega rb1000 should work well. vta adjustment would be a pain though.

Back in the 1980's when I had a Linn, I fitted it with the original Rega RB300. The decision was made following careful auditions against (primarily) the Ittok. You could do that in those days! I found the Rega to be superior to the Ittok, conventional wisdom of the day notwithstanding. Yes, height adjustment is a problem. I expect there are solutions available today that were not available at that time, but I have no experience of them.