the heater hose that comes out the manifold can it be capped off

I have a 1990 K1500 and I have had heater hose issues. I would not recommend capping it off. Try to keep everything the way it was new so you get the most out of it.

You can easily replace the connection. Most Auto Parts stores would carry it.

Let me guess, the threaded part is still in the intake and the upper part snapped off. These pos cast fittings do that all the time. You'll have to drill it out and re thread it. I recommend putting a barbed fitting to replace that "quick connect" fitting. I took my intake off to do this but it may be possible with it still on. If you cap it you won't have heat. Not that I can think of a good way to cap it

Another option would be to find a big enough easy-out tool to screw out the broken piece.