4AG = 16 valve = different port shape to 2TC = difficult (but not impossible) to fit.
I know it is not as nice as individual runners and a plenum but you could weld in injector bosses to the original 2TC manifold and use the lower section from a falcon XE/XF weber carby, on an adapter to your manifold. BTW the lower section houses the butterflies only and the original throttle linkage on the 2T carby should bolt onto the side of the falcon carby base.
thechuckster - someone must have made those manifolds as an aftermarket item for 18Rs at one stage because I have the exact same design I know it wouldn't be ideal but surely you could mount your injectors on the engine side of the runners at a pretty steep angle? As the manifold gets pretty hot I think there would be minimal wall wetting and no noticeable difference in power... anyway just my opinion.