To the good points presented by Galactic Cowboy, and, expecially, by RP, I may add only some details to confirm the sporting chance between KPR/GPR and the cypress.
1) Since the term GPR indicates also 'resin' it is obvious that that tree's kind (Gen 6:14) was a resinous one. So, the range of possible kind of tree is narrowed.
2) Other three interesting comments about GPR, (expecially that of Keil & Delitzsch, which answered the objection that in Hebrew there is another specific term for 'cypress' [berosh]):
Jamieson, Fausset & Brown: “probably cypress, remarkable for its durability and abounding on the Armenian mountains.”
Keil & Delitzsch: “The ἁπ. λεγ. [= hapax legomena] gopher is related to כֹּפֵר, resin, and κυπάρισσος; it is no proof to the contrary that in later Hebrew the cypress is called berosh, for gopher belongs to the pre-Hebraic times.”
John Gill: “[…] the cypress tree bids fairest to be the wood of which, the ark was made, as Fuller [Miscellan. Sacr. l. 4. c. 5.], Bochart [Phaleg. l. 1. c. 4. col. 22, 23.], and others [Vid. Scheuchzer. Physic. Sacr. vol. 1. p. 35.] have shown; that being nearest to ‘Gopher’ in sound, and being a wood very durable and incorruptible, and fit for shipping. Alexander made a navy of cypress trees in the groves and gardens about Babylon, as Strabo [Geograph, l. 16. p. 510.] relates […].”
3) The sound K <> G were often interchanged, not only in Hebrew and Greek languages, but in many other languages.
Here follow only some examples from Akkadian (the references are drawn by CAD [Chicago Assyrian Dictionary]):
ADAGURRU – ADAKURRU (I:1:93).
AGURRU – UKURRU (I:1:160).
AGUSIGU – KUSIGU (I:1:163).
AGAMU – AKAMU (I:1:259).
ALNINGU – ALNIKKU (I:1:364).
Benjamin Davidson (Analytical Hebrew and Chaldee Lexicon) rightly derived both terms (KPR/GPR) from the same (verbal) root. In fact, he wrote: “Gen 6. 14 גפר” i[d]. q[uod]. כפר, ‘to cover over’).
Then, the objection based on the difference between KPR and GPR has no strong basis.
4) To this point, if we hypothesize that GPR/KPR indicated the 'cypress' (considering it 'Point One'), we may build, and than close a 'Logical Circle' (including 3 'Points'). Please, follow me.
Point One: the ark (really, a 'house-container') of Noah was made by cypress wood.
Point Two: the symbology linked with the tree cypress, in all the ancient epoch, until now, and in every part of the world, assigns to this tree the concept of death, or, mourning for the dead ones. Until now, millions of cypress trees decorate cemeteries throughout the world. A WEB site (artofmourning.com) wrote, about this tree: “Cupressus sempervirens, or the ‘Graveyard Cypress’ is one of the oldest classical mourning symbols used in Western and Eastern societies [even in Islamic area][…]. Known as the ‘mournful tree’ by the Greeks and the Romans, the tree was sacred to the Fates and Furies as well as the rulers of the underworld [like Pluto, the Afterworld's Governor]. […] Here, there is a great continuity of usage for the tree, as despite its cultural interchange it still remains understood for the same purposes in death.” [you may read further information in Jean Chevalier - Alain Gheerbrant, in their Dictionnaire des Symboles , to the headword cyprès’]. Like William Shakespeare wrote, “Come away, come away, death, And in sad cypress let me be laid.” (The Twelfth Night, Act 2, Scene 4)
Point Three: The important and international holiday linked with the Commemoration of the Dead (the specific name of the feast may vary from nation to nation) just falls on the identical period when the Deluge rains began to fall (you may read further information in John Garnier, The Worship of the Dead (1904), expec. in the Chapt. 1, pages 3-11; see also the following WEB URL, htpps://aroyking.wordpress.com/2009/10/31/the-connection-between-halloween-and-the-great-flood/).
In this manner we may 'close the circle’.
So, we may conclude that, with higher probability, the term KPR/GPR (when linked to a 'tree') is a 'cypress'.