Just saw something on TV that said if you leave your ignition coils on the side, like they are on all mopar big blocks, the liquid inside pools only on it's side causing them to be less efficient, overheat and burn up quicker. Any truth to this?

That would be news to my 20+ year old "Blaster 2". Ran it in a daily driver through the 90's and didn't cook it.

Yes its absolutely true. Sure most got a away with horizontal mounting, but many do not.
Couple problems; 1) If the seal leaks, the oil will start to seep/drip. Coil will soon burn out from internal Hot spots. 2) Even if no leak, any internal air will be along the top, possibly allowing the same hot-spot condition, leading to possible failure.

An epoxy filled coil (the "Vibration-proof ones) is the way around this if you want horizontal mount.

Hughes Engines has a simple 90 degree bracket to mount the coil vertical on most aftermarket intakes. Part number AR208 on their website.

The Accel race coil that was sold thru Direct Connection was on my car for over 25 years mounted on it's side, was still working when it was replaced with a new unit "just because it was old". It's now my back up coil at the track.

oil filled coils should be mounted with the terminals facing up, just because they have been mounted otherwise without problems doesn't make it right.

i agree,i always fab a bracket to do this.

bought a coil once, side of the packaging said "do not mount horizontally" I thought "whatever" and put it on my OEM coil mount bracket. within a week, I noticed oil pooling on the intake under the coil, and wondered where that oil came from. wiped it up.

about a month later the coil was shot.

bought a new one that was more expensive, but was able to be mounted in any position, and it lasted till I pulled the engine out for restoration