The spelling of /g/ is <g>. The /ʒ/ sound is spelled <su>.
The contrast is between a stop and a fricative, both voiced but well separated in the mouth. It is unlikely to cause a problem.
The /g/ sound can occur in any position in the syllable, but /ʒ/ only occurs finally or intervocalically, other than in foreign names or loan words such as gendarme. /ʒ/ is in any case a very rare phoneme, found in only 334 words in the source dictionary.
mega measure