In the early 1970's (1972/3) I bought a Sheaffer brushed chrome fountain pen, that I recently "rediscovered" in my desk drawer along with a couple of others. One, which I'm sure is a 444xg, I bought for my father in the summer of 1974.
When I bought it I thought it was identical to my pen - same chrome, same 14k gold nib, same gold clip, but when I got home, there were a few subtle differences.
My unidentified pen is a little slimmer (about 11mm around the base of the cap, against 12mm of the 444xg. Unposted it is a little longer (121mm against 113mm). There is no metal band at the bottom of the head (with the three raised metal bits that hold the cap in place). The nib itself is also different; not the diamond, but a screw in with a little gold band 21mm or so down the barrell from the nib tip.
Finally, the converter it came with is a straight metal one, with a small button at the end, quite unlike the one that is in the 444xg. I just bought a new converter, but I don't think it will fit my mystery pen - it's too long - although it is not wasted; it fits the 444XG (and the 444, which is my other Sheaffer.
I have looked at the excellent post here: http://www.fountainpennetwork.com/forum/index.php/blog/12/entry-122-identification-help-for-sheaffer-models/ and at the other sites linked in that post, but I just can't see anything that matches.
Any help would be appreciated. Thanks.