The threaded neck on the OEM U-nit isn't any taller than the OEM bolts hex head.
1/2 inch bolt is too long though and could break gasket seal or worse..
the glass. 3/8 inch bolt length or 1/2 with washer.
In my most recent experience, I had the glass out and removed the hardware in common manner. I ground 2 threads off the OEM bolts and put them back from bottom up.