I ended up using a single intel Optane NVME as the boot drive instead of mirrored SATA drives. I’m not as sure on the HL4 but the HL8 definitely has room next to the power supply on top of the drive cage for an SSD.
I remixed for fattier drives, it works but as mentioned there is not a lot of room left between the drive bracket and the CPU… 45drives HL4/8 thick 2.5' drive bracket by havokk - Thingiverse I recommend extending the feet on the bottom of the case and adding in some 15mm thick fans to push air through inbetween the brack and CPU cooler assuming you are using the Noctua.probably wont fit with a larger CPU cooler. my use case was using a NVME>U.2 adapter, but the build had to divert from that particular design choice/placement. so the U.2 drive will go into another box somewhere.