I believe the OEM nissan has discontinued those trims and they are rare and expensive, very difficult to find... I also have the same dilemma on some trims on the car and I'm in Florida which is what I get for neglecting them.
Also, add to your list stainless steel O- Ring the block w/custom copper headgaskset, get lateral or horizontal gas ports to the pistons, have a company make you a custom girdle or custom large diameter stud (or a custom 4 bolt main stud girdle) bolt to put for main studs (something to compensate just like on v8 the 4 bolt main are the better over 2 bolt main). Maybe even a bigger wall thickness pin like .300 or .330 custom made pin size is (21mm) .827 x 2.5" x wall thickness.
Like I said earlier be prepared to pay a lot of money to end up sacrificing drivability/reliablity a 1000+HP 4 cylinder is not an enjoyable driving experience it is annoying to drive and ends up being an "on and off switch" so-to-speak (somethings got to give). It will be jerking and annoying to drive especially with large cams here an example not trying to point names or call people out just informational
https://youtu.be/jTOsJx-zGfw?t=170 .... but hey if thats what you want do it. I also have goals to build a sweet 4 cylinder engine also but I want to over build it so that I may DeTune it in the future for drifting and track racing and then detune it to make it a more fun and enjoyable driver car. But look online at some of the World record Evo 1300awhp at 67psi or something like that std dyno numbers its jerky and really only good for one thing driving in straight line..... just saying... at what point is enough- enough in power? At some point it just become a never-ending, nonenjoyable, retarded dick measuring contest..... and you just paying to scare the sh!t out of yourself risking your time, money, life etc. Then it becomes a hamster wheel of just knit picking what the engine is doing replacing bearings , damaging engines (just cause you build one good engine doesn't mean it will always last any small hiccup can ruin it catastrophic) then chasing your tail to figure out what was that noise and more knit picking sounds and random engine reactions etc you basically creating a mind **** maze for yourself and stressing yourself out and scaring yourself lol its basically a carrot to a donkey you creating for yourself. Just remember everything is easier said then done and looks good on paper or printed but there are a lot of struggles and hurdles. According to these guys they been building 4g63 for 13 + years
https://youtu.be/pwM88-9s2JcA lot of people are saying these days its more fun and better to just have a beater car for a reason. It's never any fun when your car acts like a high maintenance little prissy princess bi*ch to you all the time. You better off just getting a junk yard big block gm engine and throwing on some chinese turbos it will drive better and rip down the track better with way less effort it just flows better from factory. Maybe consider 454 engine or big v8 with chinese turbos and smaller engine as a "street car" everything past that is pretty much dick measuring contest race car ****.
Maybe even just making your car look nice and clean first is a better alternative cause they are harder to come by these days and harder to find one that actually looks nice. Anyone can make a car drive fast and make big power these days, it's wayyyy harder to find a nice clean 240sx thats not all clapped out looking different color panels dings dents paint pealing etc. there will always be someone thats faster or hooks better like EVO /GTR or has McLaren type Aerodynamics dual clutch transmission etc
Just keep in mind when hot rodding the car might never meet your performance/driving expectations but the one thing you could do is make it look nice and that might just be the one thing/goal that will satisfy your expectations.
Good luck!! If you make a ka24de custom girdle or custom main bolts let us know to get a group buy going.