Tabanus: This is probably not the Brooklyn player.
1917: Lundby chess club (Gothenburg) has elected A. Karlsson, chairman, .... <G. Gustafsson, treasurer> (Tidskrift för Schack, Feb.-March 1917, p. 55)
1917: <G. Gustafsson> wins Class III in the Gothenburg chess club (TfS, Dec. 1917, p. 348)
1918: Lundby chess club (Gothenburg) had its yearly meeting Feb. 10, and elected Arvid Karlsson, chairman; Nils Nilsson, secretary, and <Gunnar Gustafsson, treasurer.> Suppleants were Ernst Lundin and Karl Lundin. (transl. from TfS, Jan.-Feb. 1918, p. 28)
1918: Lundby chess club, Gothenburg, celebrated its 5th anniversary in Hotel Neptun. The prizes for last year was given to ... Spring tournament (1918), Class I: 1. E. Lundin, 2. F. Johansson, 3. <G. Gustafsson>. Autumn tournament (1918), Class I: 1. E. Lundin, 2nd price shared between <G. Gustafsson>, F. Johansson and R. Nylén (transl. from TfS, March-April 1919, p. 72) (E. Lundin = Ernst Lundin, and not Erik Ruben Lundin).
1920: Lundby chess club (Gothenburg) had its yearly meeting Feb. 6 (1921). Prizes were given for ... the spring tournament (1920) .. Class I: 1st price <Gunnar Gustafsson>, .. (transl. from TfS, March 1921, p. 63)
1920: <G. Gustafson> ending last in Gothenburg C (1920). (TfS, Sept.-Oct. 1920, pp. 146, 150)
1920: Lundby chess club (Gothenburg) had its yearly meeting Feb. 6 (1921). Prizes were given for ... the handicap tournament ... 5th price <Gunnar Gustafsson, ...> (transl. from TfS, March 1921, p. 63)
1929: Lundby chess club jubileum tournament, Master class ... (and) Class 1: 1st price <Gunnar Gustafsson> 5 p. (TfS, April 1929, p. 96)
1958: And now even the "strong man" in Lundby chess club, <Gunnar Gunnarsson>, has reached 60 years. (transl. from TfS, March 1958, p. 71)
1966: A message in TfS that he will now retire as treasurer in Lundby chess club.
1967: Gunnar Gustafsson has passed away. He was to become 70 next time. ... He was treasurer in the Lundby chess club for 50 years ... we remember him as a match organizer ... (transl. from Tidskrift för Schack, Oct. 1967, p. 225)
No exact date of death, but this rules out another GG candidate born 16 May 1897 (as he would be 70 already). And he was born before April 1898 (cf. above). It must be <Gunnar Joram Gustafson, born 2 Feb. 1898 in Lundby> (scanned orig. birth register for Lundby, Göteborg, fathers surname spelled Gustafson with one s)