Two beauties from the same seller:
Prinz = Yamasaki, not Rodenstock. f/4.5 tessar type <> Sironar. Unless, that is, I'm badly mistaken.
And it gets worse: http://www.ebay.com/itm/Linhof-Synch...item4606724845
The lens' maximum aperture is f/3.5, the shutter's largest engraved stop is f/4.5. The Helomar is a triplet, was used on, among others, 6x9 Bessa folders. No way will a 10.5 cm/3.5 triplet cover 4x5.
I have in front of me a 10.5 cm/3.5 Helomar s/n 2146913 in Compur Rapid #0 s/n 5317467; per P-H Pont's chronologies, the lens is from 1937-8, the shutter from 1938. The lens on offer is s/n 2180728, per Pont also '37-8.
Now we know how to transform any old lens into a Linhof presumably select one. Put it in a shutter engraved Linhof. I had no idea it was as simple as that.