Just got off the phone with Prefix and have some info to clarify with the Gen 3 Hemi aluminum blocks.

6.1 aluminum blocks are available and have been used in builds a little over 1000hp. These blocks are available through Prefix.

7.0 aluminum blocks are basically 6.1 blocks re-cast with additional reinforcements and "X" bracing on the blocks. Made primarily for the 2016 354 cid and 426 cid Drag Pack Challengers, most all have been already sold and Prefix cannot get them.

6.4 aluminum blocks are a new release from Mopar made for the Factory Stock drag racing series and have relocated oil pick ups and require different oil pans among other changes to accomodate for VVT options.They are so new that even Prefix is not able to get them but may be available through your local Mopar dealer.