Josh, I'd like to hear that you have pulled the starter , cleaned the commutator and brushes and made sure the brushes floated freely in their holder . A bit of lube on the bushing too
Then I have an observation.
On all my 6 cyl chev car/trucks, the #1 plug lead goes to the 4 o'clock position on the dist cap. I see yours goes to the 12 o'clock position.
I have no idea if this is influencing your lack of go , but that's a thing I see.
Did the bigger cables help spin the engine faster? It sounds REALLY slow on the vid.
I have used 12v on my truck for over 14yrs. just short stands on the starter. It's ok.
For me, short stands is 3 to 5 seconds , if it hasn't started by then , there is a problem. (latest being weather related , damp in the dist cap)
Compression pressures I have noticed range around 110 to 130, for an engine that drives fine, but its more important that they are all similar , say within 5 pounds of each other.
Remember to have all the plugs out so it spins freely when doing the test.
