So i was able to speak with CX Racing customer service.
I spoke with a representative who was familiar with the LS / S30 platform and he said that on 280z's since the trans tunnel is wider, you would only use the front set of adapter mounts, and not the rear mounting tabs that required drilling to the seatbelt hole / trans tunnel area.
For the motor mount issue, i sent them an email with photos and they told me they'd review the photos, and if there was an issue with the mounts they they'd send me a new set. Not bad so far! Keep in mind that my mounts were purchased about 4 years ago, and they are still willing to look into this issue for me. I'll keep everyone updated, but so far my experience with CX has been good and responsive so far.