Help with a ladder rack

Need an over cab rack to carry 300 pounds on my silverado.  Found a decent used one, even set up to work with a cap if I ever need one of those too.  Started mounting and am seeing all sorts of things I don't like.  First off, wanted to mount the uprights in the corners of the bed rails but the silverado bed doesn't have access to the inside of the rail for tightening the nuts.  I can slide the uprights in a bit from the corners, but this looks goofy.  Do I get out the grinder and hole saw to make some access holes?  Other issue is the height of the cross rails over the cab.  There is over 6 inches clearance, from the bottom of the cross bar to the top of the cab and I cannot think of a reason for so much gap.  Before I start cutting the upright to lower the rack can someone give me a reason why this would be a bad idea?

I just ran into the same issue with my B4000.  I'll show you what I did and it might help you.

The fronts were fine, although I had to drill an additional hole in the baseplate to fit in front of the stake pocket.  For the rear I drilled the side of the base rail and into the stake pocket.  Then a welded a 3/8" bolt to a short strap of steel and poked it out from inside the stake pocket through the side of the baseplate.  You may need to space it depending on how your bedrails extend past the stake pocket

Another option could be to fab up some kind of speed nut, toggle nut, or plated nut that hides down in the stake pocket.  Kinda like my welded bolt idea above, but vertically down in the stake pocket hole.  You could weld a nut to some angle or flat bar, glue a couple magnets on it so that it sticks to the bottom of the stake pocket until you can get a bolt started in it.

As far as the height is concerned, yeah... its a bit of a bummer.  I'm not too unhappy, but some day I might hack about 5" off of mine.  For now I'm living with the trade off of easier in/out with the taller headroom vs. big tall ugly rack.  They have to make them so tall so that it fits the tallest truck cab on the market with room to spare.  Some come with an extender piece for two possible heights, but I didn't want the extra joints and failure points.

Thanks.  Your idea is helpful, also watched a bunch of utube videos and looked at all sorts of rack installation videos.  Currently thinking of cutting the mount plates off and making an adapter to put the legs in the stake pockets.  Looks like it will drop the height to an inch over the cab roof and make for a stronger mount.  The current mount plates are only a few inches wide and the bed rails are rather thin.  Using the pockets seems much stronger.

I have the same thoughts as well.  I also considered just hacking about 5" off the uprights and re-welding them to the base plates.

Pics when you're done.  I might steal your idea :)

And as far as the 300 lbs thing... mine is rated for 800 lbs as are most ladder racks.  I think you'd really have to botch it to make 300 lbs a danger.  I frequently carry 10-16' lumber and I used to have an 8' bed... which was ok for the 10' and maybe the 12', but nothing short of a box truck or big flatbed would take the 16'.  So I think I found the best of both worlds; a smaller truck that gets decent mpg, easy to park, but can now carry 16' with ease.

Just last week I carried six 2x6-16 sticks of PT up there and it handled it fantastically.  Curves were a bit fun with the weight way up there, but I watched in the mirror and the uprights didn't budge.