Overly above idle condition

No, a headgasket won't cause that to happen. Check to make sure the idle break solenoid is working properly. Also, since the vehicle sat, check to make sure the choke isn't moving around on the carb while running. As far as the oil in the radiator, make sure it is motor oil and not trans fluid. The cooler may have rotted through. If coolant gets into the trans, it will destroy it.

Hi Jacobandnickolas, fortunately, I hadn't poured coolant on the radiator as of yet since I was still in the process of flushing it after having had replaced the timing chain, timing cover and water pump.

Thanks to your advice, I went ahead and isolated the cooler section off the radiator, capped off the bottom radiator line thread and applied a bit of compressed air through the upper end and noticed air bubbles inside the radiator which proved your theory correct.

I have continued flushing the radiator, thus becoming oil free.

I drained the transmission fluid and inspected the trans oil pan
with no apparent water mix.

As far as the above idle condition, after it reaches normal operating temperature, the idle feels normal; however, there are instances that while accelerating either at cruising or short stop, it accelarates above normal by itself and by sudden quick pushing and deppressing the accelerator pedal it releases from above idle back to normal.

You had mentioned the possibility of the choke being moving around inside the carburator.

If that's the case? What may be causing that and what should I observe and adjust or replace accordingly?

Prior to this, I cleaned out the carb., installed the lean mixture screw repair kit and the carb repair kit and replaced the secondary Choke Pull Off.