I still think they will fill. I just checked a MT cover I have here and the holes measures 1.410" and I just had the grommet in it the breather is very tight.

I bet you 1.5" is going to be OK? Unless you already tried it, then your screwed and must weld up the cover and redill if your handy with that kind of thing.

Otherwise get another valve cover unless ford or chevy uses 1.5?