vertical holes in 2x4" frame?

[billy]

i need to drill four 1/2" holes all the way through my 2x4 frame
top to bottom.
there will be bolts going through to hold the cab of my truck to the frame.
will that weaken my frame considerably?

[billy]

i have these plates that are 2" x about 6" 1/4 inch thick steel  i am using for washers

[Coley]

Holes in the top and bottom of a frame are not usually as bad as holes in the sides.
Are you using pipe spacers inside the box area so the top and bottom are not pulled toward the center?

One way to do this is bore the top hole as large as the spacer and weld it to the spacer after cutting it to length.