Overheating 360 new engine

Your fans are rotating in the correct direction ...... right?
Do this;
At idle and over 180*F
First check the temps of the water across the rad from where the coolant goes in to where it leaves, looking for about a 30 degree difference. If you get close to this; STOP! I'll bet you a box of dirty doghair that one of two things is wrong;
1) you have insufficient idle timing, (or waaay too much but that is near to impossible at Idle)
2) your rings are gapped too tight and or you need more skirt clearance.

As to #1,
if your timing is too retarded, the A/F mixture will not finish burning high enough up in the chamber, and will instead continue burning as the piston goes down. The blow-down heat now goes into the water jacket thru the cylinder walls, instead of out the exhaust system .
If you have headers; at idle,you should be seeing temps in the primaries of about 400*F +/- 50*, At 450, the mixture is still burning in the ports and head pipes, and heating up the heads now. At under 350, I'll guess she's running really rich.
So here is a test;
With the engine over 150, just advance the timing without regard to the numbers. As you add Idle-timing, the rpm will go up. Keep adding timing until the rpm no longer rises. If it goes over 1200rpm, put it back a bit. Now put a Timing-light on it and back it up 3 degrees. When the temp gets to 200, turn both fans on;
Now watch your temp gauges.
>Here's the deal, your engine, at idle, wants a ton of timing. By the rpm rising, she is telling you that she is making more Idle-Power. Since you did not adjust the AFR, this can only happen if more of the pressure produced by the expanding gasses, is being delivered to the crank at the optimum time, measured in crank-degrees.
Now, withe Idle Timing out of the way, and the rpm back to normal, the heat of combustion should be exiting at a normal temperature and your overheating issue should be gone.
Keep watching your temp gauges.
If the temp keeps rising, then Idle-Timing is NOT your problem.

Ok, so
With the fans on full-time, the coolant temp should drop back down to the thermostat setting. If it does not; check the following;
>the rotation of your two fans are both in the same direction, and
that the air is going in the right direction, from the front of the car to the engine side, and
>that the air is coming thru the rad, and
>is not able to shortcut back to the front side, and
>has an escape route under the car.
>That the lower hose is not sucked flat,
>That the thermostat is opening,
> that the coolant is circulating,

As to #2,
When all else fails to bring the issue to light;
you gotta consider that the engine itself may be creating internal friction, beyond the norm. That friction comes almost exclusively from the rings and skirts, with a portion added by the valve springs.
So go back to your build spec, and check those clearances. Then compare them to what the builders on FABO recommend, for the piston and ring types that you are using.

Happy HotRodding