This poly block has four 1″ ports on the bottom and one 1″ port on each side each with NPT threads. You can plug the ports not needed with 1″ plugs. It also has 4 holes drilled for mounting.
You can downsize the ports to build 3/4 proportioners for air or 12V systems if needed.
1″ Plug https://www.grainger.com/product/GRAINGER-APPROVED-Hex-Head-Plug-1-in-Pipe-Size-1MKA3