Grab the back of the xfer case and see how easily it moves side-side. I'd bet the motor mounts are shot too. Might want to fix that oil leak at some point as well.

 

I've seen instances where the bolts that go UP into the adapter housing from the trans mount are gone.

 

shockingly, its very difficult to move side to side. very little movement.
classic oil filter adapter leak, have degreaser and rags, have the kit to fix it just only now getting around to it with the weather being nice (hot)
have no high heat gloves apparently so just gonna grab the exhaust clamp w/ hook on it for now as a hold off of new exhaust being the last of my worries currently

I did more toying today and have some good and bads
Good:
U Joints are 'fine', no play, as good as they can be for old u joints, no movement at all and can easily spin rotor with 1 hand while straight, turned left, and turned right.
Bad:
Track bar and drag link ball joints are all shot. Going to take a gander around for replacements.
Wheel bearings are possibly shot? they dont feel rough and dont make a clicking noise while driving slow, no tell-tale signs besides the low rumbling while doing 45->90 degree left hand turns
which brings me to my next question
Front Differential: Could this be the source of the rumbling/grinding while in park idle/shifting? There is the small amount of rotational play with the pinion and ujoint look good, no play forward/backwards, up/down; which makes me think the gears inside the diff are worn severely. I had this issue a while back and doing a fluid swap I saw no glitter or shavings but I did not take off the cover to inspect it completely. Really hope that isn't it...

Would like everyones opinions on this and how they would move forward because currently I am trying to figure out what to address first, probably ball joints.