The /ʊ/ vowel is spelled <oo> or <u>. The /ʊə/ diphthong is spelled <oor> or <our>.
This is a contrast between a short vowel and a diphthong, with the same starting positions. There is potential for confusion but so few pairs that it does not constitute a problem.
The density figure is 0.28%. The set makes 2 semantic contrasts giving a loading of 67%, though that is insignificant in such a short list.
good gourd goods gourds pulley poorly
John Higgins, Shaftesbury, December 2009