Fitting a Weatherguard box into a 95 Pickup (not Tacoma)

I figured a crew of Tacoma/Tundra owners might be able to steer me the right way since we're so close in vehicular profile here. I have a '95 Pickup (remember the split year?) with a standard bed. I'm casually shopping for a chest to put in the bed that will A) maximize the amount of space inside the chest and B) not lay on top of the bed sides (I have mounts for a canvas bed cover installed).

It looks like the Weatherguard 654-0-01 model fits in a standard bed Tundra, and by most measurements will fit my bed as well. Where I'm uncertain is the fit between the front wall of the bed and the wheel wells. I measured the run front-to-back in my bed to be about 14". Weatherguard posts their box to be 20" wide, but this is not accounting for the slanted cutout at the bottom which is designed to fit against the wheel wells. I called them to see if they had more detailed measurements for the width of just the bottom, the length/pitch of the angle, etc., but they couldn't provide me with any more measurements than were already available on their website.

There's no place I could find where they're just lying around waiting for me to approach with measuring tape, attempt to drop in, or ask for a refund if something doesn't fit right. So, before I go and spend any money on a box (new or used), I wanted to know if it would actually fit. If this is supposed to fit in a Tundra, might it fit the Pickup? If anyone here has one, would you be willing to run tape and tell me how wide (front-to-back) the bottom is, excluding the slanted cutout? Let me know! Do you maybe have another suggestion that may work for me?

 

This is my Protech I had made for my 2011 Tacoma. Not familiar with the dimensions of you bed (pictures might help). My box is 56"x 20"x 10". Protech offers custom services. I started with a box that is in there RV line and just had them make it 56" long instead of the 60" that is there stock size. Understand there not cheap but you get what you pay for.