Hi, Sanma. Nice to see a question about such an obscure prop!
To my knowledge, there has never been a discussion about this, here at The Raven. Nobody has answered you, so I will.
The other 'boards' you refer to are most likely correct. As a former calligraphy instructor & enthusiast, I do know a bit about classical writing instruments and after doing some in-depth
analysis on Henry Sr.'s pens, 1 of the 3
associated with "Crusade" does indeed appear to have been a
Conway Stewart #58, which is a top quality choice!
However, it's presence in 1938 is yet another anachronism for the film series (even though it's a very, very, very
minor one).
Henry Sr.'s three (excluding the TV series):
1) The pen used in Utah
2) The pen used in the tank
3) The pen not used/seen in the film
(as far as I can determine)
Each of these 3 can be elaborated upon but, for the moment, here's a scan
* from the book, "The Best of the Lucasfilm Archives", which shows 2 of them. Details will follow about Henry's deft,
ink-squirting manoeuvre & which pen he used to pull it off...
*Larger than actual size.
One thing's for sure is that they ain't Sheaffers.
To identify that brand: "Look for the white dot" (as the TV commercials used to say.)