The 1981 ute A12 and A14 engine use the same mounts (only the before-1973 engines use different mounts).

Reportedly the extractors/headers from any A-series engine will bolt on any other, though they might have a different size pipe. The A14 is taller, so there is a small chance that your exhaust pipe will hit the firewall, but that can easily be fixed. Also, there is some chance the headers may not fit with the A14 inlet manifold which has a different shape.

Yes, you will use far more fuel with dual carbs for two reasons. As demojob says, dual carbs on a stock engine won't be better; they won't give you any more hp than a single 32/36 or G180 carb.