I am not familiar with that particular model, but on my 2GM20F you have to take the pump off in order to inspect/replace the impeller. There is no room behind the pump to remove anything, although the front is very accessible making removal not that tough.
It at least sounds like you can get to the back of the pump. Still, removing those small screws won't be fun. What I suggest to make removing the back cover plate at least possible is a Speed Seal. Made in Britain. It replaces the cover plate with a milled stainless piece that then uses 4 large knurled knobs to hold it in place. Unscrewing the knobs is a breeze compared to messing with those small screws. The Speed Seal also uses an O ring for a seal, doing away with that idiotic paper seal on most raw water pumps. You still have the issue of using a mirror or whatever to get to the impeller itself of course, but at least you can get the cover plate off without losing your religion.