I don't know if the bolts are compatible but I hardly think you are out of luck. As far as I know GMC doesn't make their own bolts and I am certain that bolt manufacturers would not make bolts that are exclusive to any particular engine. In other words I am certain there is a lot of compatibility.
I know the GMC rad has the hole on the side of the tank whereas the Chevy hole is in the centre. If that makes the thermostat housing different I could not say.
There is a good GMC truck site on the web and they could probably tell you more and they have a swap section where you might find the housing.


1949 Chevy 1/2-Ton
"Sedgewick"
In the Gallery
1989 Caprice