Update:
Worked on the cooling system today:
I pulled out the stock rubber rad hoses - they looked like they hadn't been changed in a while.
My heater core leaks, and the previous owner in Japan only plugged the heater core hoses - but didn't remove them.
It's summer time & it's isn't going to get cold in SoCal for a while, so fixing the heater core is way down on the priority list.
I simplified the plumbing and did some compare contrast with the Z...

The front coolant fitting for this L28 block is different than it is on the Z's, as it angles back instead of outwards.
I am guessing this is the original L20 Skyline front coolant fitting that was re-used when they did the engine swap on this car.
If you swapped out to a Z front coolant fitting, you can then use Z coolant hoses fyi as the hose diameters are the same...
The gaskets are the same for both fyi too
(Part number below for the fitting)

_ FYI On the Skyline, the smaller pipe fitting that comes off the front fitting (this is the heater core inlet I believe) requires a 3/4" hose.
_ But about a foot front the front fitting, there's a reducer that steps it down from 3/4" to 5/8" and this second hose goes to heater core.
_ The 90" coolant fitting at the back of the engine and which goes to the heater core outlet is sized for a 5/8" hose.
_ So if you are going to keep the Skyline front fitting, you should consider buying yourself a 3/4" to 5/8" reducer because your stock Nissan one will probably be pretty corroded - mine was.
_ If you swap out to the Z front fitting, the heater core inlet pipe is 5/8" so no need for a reducer!
While I was at it I also swapped out water pump and flushed the radiator.
Then, I noticed the 12" Perma Cool fan the car came with was loose... that's promising!
When I looked closer, I noticed that 2 of the 4 PermaCool plastic "L" brackets were loose / broken.
At speed, that meant the fan had gently eased into the water pump pulley and there was a noticeable round wear groove where the pulled had been rubbing on the plastic fan housing... yay!
So I removed it, and instead decided to go with two smaller electric fans with each one on a specific relay - a little bit of redundancy in case one goes down... I can still struggle home... I gained clearance with the water pump pulley too
