My VC1 will take Feather blades without any mods or the Gem with the spine removed. My VC2,VC3and VC4 take the feather without mods. As Dick says I believe some just don't fit but they are in the minority.
I'm sure pjgh will show and blow us out of the water with his knowledge.
btw the VC1 is one of the best shaves I've had, but all the models all shave differently imho.
Gaz