Once the bodies and manifold are done they can be brazed.
The fit should be a good sliding fit so the braze material can get through. After fluxing everything I set the valve bodies in the manifold leaving them slightly away from the front surface so I could get a little braze material in there if there was any problem but the material ran through and the bodies would suck up to the surface.
I used a 1/32” silver solder wire which makes it easier to control. Keep the heat on the big part and probably using propane is a good approach.
I had sandblasted the manifold to see what it would look like but I taped everything and sand blasting it again to clean everything up after it was done. It gives it a nice almost casting look.