Can an iPod (MA146ll) 5th generation, fit into a 7th generation case?

Maybe.

The 5th gen 30GB version is just a tiny bit thicker than the Classic. The 80GB version is quite a bit thicker, and the case is not likely to fit. If the case has some give it may work with the 30GB version, otherwise, its gonna be a very tight fit or won't fit at all in the case of the 80GB version.

Height and Width are the same between both models.

Fifth Generation iPod (Late 2006) - Technical Specifications

iPod classic 160GB (Late 2009) - Technical Specifications

Hello,

Those iPod models have a different case size.