Wheel hop in REVERSE?

The driveshaft always goes downhill away from the trans, and the angle is always very shallow. As long as it is at least 1* then she's good to go. This 1* is strictly to to keep the needles shuffling around to not dig grooves in the crosspin. The angle can be more but there is zero reason to make it so, leave it alone.
Bolt the K tight to the frame without shims and
put the engine down on the mounts where it belongs, then
solve your engine clearances in the usual ways.
If you use all the proper factory parts, then it will fit with little to no fooling around.
As for the pinion angle; the softer your rear springs are, the more the engine-torque can wrap the pinion up. And if it goes just a lil nose up it makes a lil vibration. If it goes a lot nose up, it makes a lot of vibration. setting the pinion angle is in compensation for the springs. The snubber is also there to help control wrap-up, but should not be used only for that. Put the right springs on there for the torque the engine produces.
Playing with the pinion angle will not solve your problem.
IMO you have an engagement issue, probably aggravated by that jacked up trans mount behaving like jello, which may be modulating the Z-bar, and thus the TO fork, and thus the clutch-chatter.
After everything is returned to the factory engineered specs, and this includes especially the Z-bar orientation,then
the root issue will probably end up being clutch chatter due to contamination, or a warped flywheel or pressure-plate,pp.

BTW, raising the tail of the trans is totally the wrong way to go.

Keep in mind that the GROUND-PLAIN has nothing whatsoever to do with setting these angles. All settings are relative to the driveshaft. Nose down at the pinion means relative to the driveshaft. and the driveshaft must always go downhill from the trans. If you increase the rear nosedown, this will automatically increase the trans angle.
With my HO 360/CenterForce clutch/3.55s, the pinion angle can easily be varied 3 to 5 degrees with the vehicle stopped and the Line-loc set, simply by slipping the clutch. First the snubber will lift the car I'll guess over two inches. When the tires begin to spin,the pinion drops, and the rear deck falls. From there I can do anything with the gas pedal I want, and none of this monkey motion produces wheel-hop, with any tire I have installed back there.
Now; The engine is wearing factory biscuit mounts up front with a Schumacher engine tie-down. In the back is a poly late style spool mount, Slightly lowered for GVod clearance; maybe .25 inch at most. The rear has been lowered by de-arching the springs. and it wears 295/50-15s back there which are about 27" tall. The front was lowered as well to have a slight down-rake at the front. The K is about 5.75 to 6 inches from the road. So the snubber is very very close to the floorpan. What I'm indicating here is for comparison to yours.
I installed a second mainleaf at the back, full length, minus the eyes of course. My engine seems to make a lotta lotta idle-torque, cuz she's a dump-it and go deal at take-off with a starter gear of 10.97. I don't recall what angle I ended up with at the back, but probably in the range of 3 to 4 degrees, cuz she's a streeter. and traction-limited. Not to mention the leafs are really really stiff. There were times I had to remove the snubber, cuz it was pounding out the pan.Actually, I might not ever have put it back in after the drags in 2004. lol.Hmmmmmmmm