Silentblock rear on gearbox 330 serie II

[daffy]

I orderd a new silentblock for my gearbox at Dennis MCcann. The one I got has a 14mm senterhole in sted of the original 16mm. I call Dennis and he tells me to change the bolt to 14mm and put some bushings in the mountingbracket. But since this is the only point where the gearbox is mounted I am a little afraid to change dimmention to something weaker.
Has anybody done this. Will it hold ?