this is long, but please bear with it, it will make sense.
Mareo this is not personal, so lighten up a little will ya? you are frustrated with a problem you can't figure out, so you asked those who are here for help, but it seems that you don't like the answers you are getting, WHY?
first off you are using the wrong plugs, please get a second opinion to confirm this, Nissan specified BP5ES for the A series with point ignition, BPR5ES-II for electronic ignition. BP5EY is for toyota's and honda's NOT NISSAN, again I beg you to have someone else confirn this.
despite how it might appear, I DO NOT claim to know everything, no one does, we all make mistakes, me, you, everyone.
stop and think about a few things, then go back to the basics. a restrictor plate works great for a race car, but isn't very practical for the street, why? very simple a thermostat is there to regulate engine heat, as in keeping warm water in the motor until it reaches normal operating tempurature, after the motor warms up, it also controlls the flow of coolant TO PREVENT OVERHEATING. if the coolant does not spend enough time in the radiator to allow it to exchange heat and cool off, IT WILL CAUSE AN OVERHEATING PROBLEM., go buy yourself a 160 degree thermostat and a new gasket and put them into the car and run it, maybe it will help, maybe it won't, but it can't hurt to try, at least you will know for sure that this is not the problem. with as big as radiator as you say you have you should never have a cooling problem.
you say you tried water pumps, radiators, flushes, etc., etc. and didn't get results. the only other thing besides the carb you haven't changed is that restrictor plate, or so you said, could that be the problem?
again, NOTHING PERSONAL, we are all here to help each other, not get into pissing contests. I've doing this for the better part of 30 years, and have seen a bunch of things cause problems like you are experiancing, problem is that I don't know you, your background or you car so I do need to cover all the seemingly stupid possabilities just to make sure. I could be way off in the ozone on this, but please think about it.
in re-reading your last post, I have a few questions, what motor (as in A12, A14)?
what compression ratio are the pistons? (stock dished, flat tops, domed) which cylinder head (casting number H10, H23, H62, H72, etc.) has it been bored?, with or without a heater (yes this could make a difference) what cam? is it possable that the cam timing is a tooth off? (see this all the time on belt driven motors) I ask that one because you say the timing is set at TDC and you still get ping, could be that the cam is advanced 1 tooth and causing the problem. I have ran A12's at 25 degrees advance flat out hard on pump gas and never had a pinging problem.
it sounds as if you have covered most of the obvious stuff, might be that you are going to have to start taking things apart and verifying that the mechanicals are where they need to be. if that isn't it and the motor has been bored, could be that the cylinder walls are too thin, this would have been caused by core shift in the block casting.
good luck.