The /u/ vowel is usually spelled <oo>, <ew>, <u> and <o> in two. The /ɔɪ/ diphthong is spelled <oy> and <oi>.
This is a contrast between a long vowel and a diphthong, fairly close in starting positions. It is not a recognised problem for any group of learners.
There is one taboo word pair, coon/coign.
Interesting pairs include:
allude alloyed
coolie coyly
looter loiter
The density figure is 6.38%. The set makes 24 semantic contrasts giving a loading of 48%.
allude alloyed boo boy boos boys boo buoy boos buoys booing buoying booed buoyed booze boys buhl boil clew cloy clewed cloyed clewing cloying clews cloys coo coy cool coil cooled coiled cooling coiling cools coils coolie coyly coon coign coons coigns coot quoit coots quoits fool foil fooled foiled fooling foiling fools foils gnus noise Jew joy Jews joys juice Joyce June join Junes joins loon loin loons loins looter loiter looters loiters noose Neuss rue Roy sou soy spool spoil spools spoils too toy two toy twos toys tool toil tooled toiled tooling toiling tools toils true troy
John Higgins, Shaftesbury, December 2009