Leigh I was peed off at your opinions and biased rants because that is all you had presented and they mean squat.
The past is not just on the net for me and you werent around or knew why the Zet has got some of its rep with the L crowd. To hear you say its a dud motor/head especially when others are using it with good results, not to mention Nissan chose it is simply lame.
You havent been the other side of the coin by just stabbing with your opinions. Opinions are great but not just plain biased criticism with no reason or experience and total disregard from the start to the requirements or criteria of Ruredis quest.

The Zet comments didnt come from your experience and the "age" was to let you know I and family have been doing it for longer before you knew what a nappy Z head was.
As for reading the internet daily I dont even have a facebook account or my own mobile phone (i sometimes use the wifes as I hate the things) or a thread as long as your project threads. My focus now is on the Quacka head CA for Ive invested too much time on CA bits and will try and make time for it but so many things get in the way when you are 40+ and had bigger projects 20 years ago where time was available.

Belittle the Z head without your own experience splash crap at the Z18et owner(s) and expect the same from me thats who I am intolerant of crap or disrespect.

Do you remember skipping work to pick up the weber manifold from me in 2003 from 7/11 on bell street? Mate you asked me more questions than LA Law yet I was happy to help even though it was me me me from your side. My memory is pretty good and my collection of car and motorbike books articles, attendance at all kinds of modern and classic motoring events with the family and friends has made me open minded and knowledgeable in all areas/brands of motoring.

Ruredi doesnt have to go the z head on the L block but his requirement where to be as lightweight as possible, engineer easy (room for more capacity), old looks and affordable bolt on accessories without too much clutter or wiring which an L head would create with inlet and outlet on the same side.
If the height of the L head was shorter Id recommend it with manifold runners sitting over it with inlet on other side.

If there was another nissan combo that met so "many areas"
Im sure Ruredi will be happy to hear about it.

As for A12 weight vs Z18et weight...
A12 fully dressed no liquids is about 108kg from the ones Ive freight and had freighted to me. Thats about 10kg lighter than Z18et supposedly at 118kg. Heavier box by 20-25kg and heavier h165 diff another 10kg? theres almost 40-50kg yet lightweight fly/clutch -6kg, better manifolds -3kg? and lighter L16 block -15kg with 3kg heavier crank makes the total around 20kg heavier than stock +/- 10kg.

Diff is going to be an issue as LSDs are not easy to find unless you get a Top Gear one but I think the power will suffice as long its a cast iron carrier centre.

There is one other engine that could be used but made by Prince and sitting at Ferals place a g18 or even better a G20 but dont expect to find one in Oz easily :(