Weld on yakima / Thule bars
I had Larry Remuda weld two 6" Yakima bars along each side of the top bars, so I could mount paddle keeper or bike mounts. Here are a couple of other suggestions:
For a side Kayak /Bike mount, weld a female pipe onto the vertical sides of the rack, so you can fit 1' yakima bars into the side of the rack- secured with a cotter pin. Then you would have non-permanent bars to secure a boat on the side, which you could remove so that you don't decapitate yourself walking around your truck.
Be mindful of the placement of the front bar if you extend the rack over the cab. It should be a little forward of the top of the windshield- if it's directly over the cab, the wind resistance can cause a hell of a lot of noise. If you want another crossbar between the front bar and the capper, have the welder install a removable crossbar over your cab so that you can leave it in the garage most of the year. The only time you need the bar up front is when you're carting 12 boats around.
Don't go crazy on the tie-downs. With straps, you don't really need them. I didn't include any on my rack & the only place I wish I had them is right near the front, where the bar wraps around the windshield. Sometimes the straps can slip around that bend.
if they can, get them to run wiring for a light mount in the bars so you can set up a floodlight for the back of your truck.