Jack Clifford developed that intake decades ago. The originals did not have provision for water heat to the bottom of the intake. The new versions have had that provision for quite a few years now.https://cliffordperformance.net/store/ols/products/42-4500wh-chevy-235-intake-manifold
Yours looks to be one of Jack’s original design i takes with out the water heat.
You will have to do a little bit of tuning to get that carb dialed in, same for using the small 390 Holley, but once dialed in, that set up runs pretty good.
The bottom of the intake has a little open chamber. You can weld a plate with fittings to make a water chamber. Then run hot water from the thermostat housing, Stovebolt Engine Company sells a lower housing with a water outlet on the driver side, or dig up a 270 or 302 gmc lower housing. They will have either a boss that can be drilled, or the boss already drilled and tapped. The hot water helps keep heat on the bottom of the intake to assist in vaporizing the fuel.