how to make a 6.1 spin safely 7500 rpms?

Not sure what your "build from scratch" tally is going to be, but there are some pretty affordable 392 short blocks on the market... wink wink

Fully forged
ATK HPE-SP97 Gen III Hemi 392CI Stroker Short Block Flat Top Pistons - 32 Tooth, Pre 2009

Last i checked a forged rotating assembly alone was $3000...