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Finished up work a bit early today so decided to go for it on the new mounts.
I had some blanks laser cut a few weeks ago - I measured them so they would nest onto a Pontiac/Olds clamshell lower mount. These also fit towards the center of the block, unlike the Chevy style which are forward. If you pull the trans the motor will balance on the mounts - Chevy's will not.
As you see there are several punched holes for the different types of mounts.
I bolted up the plate to the block with a pair of bolts, not all 4.
The ears were retained with a motor mount bolt, which will need to be longer to work. I put a thin washer in between the rear plate and lower mount to give about 0.075" slop on the ears during fitment.
I raised car as high as I could and still be able to lower the motor. I slowly lowered it till it sat roughly cradled in the V's formed by the ears.
Fore/aft alignment was checked, as was side to side levelness and place a large framing square on the flywheel and gunsighted the differential so it was aligned longitudinally.
After 20 minutes of fiddling I pronounce it ready and tack welded it.
As you see by the above pic, the ears rest on the clamshell's inner metal ears, as God and GM intended...
Once that was done, the bolts, nuts and washers were pulled and the car lowered and the motor raised to clear the front with this being the result.
I will weld it final, then bevel the inner ears and maybe open up the interface bolt holes for easier installation.
The LT engines use a PCV / Air Oil Separator tank just behind the water pump that has a drain that goes in to the oil pan (the drain plug on the passenger side of your oil pan) it's in the picture you posted. The motor mounts can come into play when re-plumbing that system, which is why I asked that question.
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L84/LT1 motor mount alternative 
