LA 360 high idle

Well that is a classic sign of a confused carb., with a way-off T-port sync. The throttle blades are open just far enough that there is a strong enough signal to initiate a dribble through the boosters. The transfers are flowing and so are the idle ports. The mixture screws make almost no difference where you set them, cuz the percentage of fuel that they are now delivering is so small in relation to all the other fuel flowing through there.
Now when you eliminate the air flow thru the carb, the engine rpm drops to where it wants to stall, same as if you had shut off the key. But if just before it stalls, you again introduce the air, now at the reduced idle speed, the air flow thru the boosters has quit and along with that, so has the booster dribble. So the carb idles normally for a few seconds. Then because the throttle is still so far open, the rpm rises and the cycle begins anew.
The usual cure is to increase the idle-timing and shut down the curb-idle screw, restoring the T-port sync.
The kicker is if the intake is sucking air from elsewhere, unregulated by the butterflies. Then this situation does not arise. In fact;usually the opposite. The blades may be closed down waaay too far, to the point that the transfers are barely flowing enough.
And another is if the vacuum advance is hooked up directly to manifold vacuum, and there is enough signal-pull there to begin the advancement. As soon as the engine develops enough vacuum to activate it, the rpm rises, which increases the signal, which increases the advance and so it goes until all the vacuum advance is all in and then the idle speed stabilizes at a new higher,usually much-higher rpm.This can also,allbeit rarely, happen with the Vcan hooked to ported vacuum, a retarded idle timing, and much too-far open throttle plates; required to keep the poor thing running.
So once again, starting with a T-port sync, eliminates a lot of problems.

Now lets talk about the leaking water port.Is there any chance that you forgot to slot out the bolt holes in the intake, which would make it possible for it to slide down,or up, as the case may be, in compensation for any engine machining, such as decking,shaving,surfacing,or angle milling? And did you follow the intake torquing program? You know; the three-step circle pattern.
Happy fiddling,lol