injection would be easy with injector machined on the back using brass tabs and would face direct to the ports.

To create these units it would need a separator going up to halve way up to keep pulses even similar to stock manifolds but angle and port size should be increased for more volume and top two inlets at about 44 to 50mm tapered so if someone wants to run smaller carbs just cut off lower on the inlet pipes but must have a step on the outside for ease of securing hosing or sliding bigger alloy pipe on top for welding but those things can be also machined later.

These kind of mini manifolds would allow better turbo manifold design or straight out exhaust pipes.