no-one has mentioned a plate system.
To put Nitrous Oxide onto an A15, you will need to run an aditional fuel sytem. The secret to a good reliable system is a sound unvarying fuel supply.
The easiest way to install nitrous on an a15, would be to make a carb spacer plate and fit a single fogger nozzel to it. you can adjust the HP increase by changing the saphire jets.
The disadvantage datsuns have is a tiny fuel supply line from the fuel tank. I don't know if an extra fuel pump teed in before the factory mechanical pump would be able to supply enough juice. Bear in mind that if fuel pressure or supply volume is too low, (Or drops will you've got the squeeze on) the resulting lean out will melt your pistons.A mate of mine had this the first time he squeezed a brand new drag engine. He said it looked like the pistons has been disolved by acid. You also need to use spark plugs with a fat earth strap. Thin ones that protrude too far into the chamber will contribute towards preignition.
Nitrous engines like a camshaft with quite a wide lobe seperation angle. (112'+) Due to the increased combustion gases the exuast valve needs to be opened sooner before BDC, so that more of the energy of the expanding gas can be used to aid the evacuation of the spent charge. The upshot of this type of cam profile is that off the bottle perfomance will suffer.
I dont think that for 50 hp shot you'll need to worry about changing the cam. A single fogger kit should provide details of what jets to run with different fuel pressures.
I plan to bottle feed my s/cA15 down the line. A mate has an old plate system with no bottle he said he'll give me. I plan to buy a kit for my V8, so the two cars can share the bottle.