a few things I noticed during playtesting:
• the timeshifted cards are fun but they are mostly extra bombs and 48 are just too many. Cutting back down to 24 for further testing.
• from playing my other set cubes I've learned that commons can have three copies without being omnipresent. In real booster drafts or sealed you sometimes had two or even three of the same common in your cardpool.
• I am considering cutting a few uncommons that are straight up bad like Chainer's torment and bumping others up to two copies...

Cubecobra seems to be bugged as it currently wants to cut 4 copies of aesthir glider from this list while I only have two in it. I'll have to see what happens when I apply the update and probably will need to post an addendum.

It wasn't easy figuring out how to rebalance the boosters to not only include two extra timeshifted slots but also add 3 extra boosters - 45 cards - to support another drafter. When I noticed that the original format didn't have enough playables to reasonably allow for 8-player drafts I first went down to 315 cards. Wow adding timeshifted cards for variance and size. I know some people don't like breaking the 'feel' of the original format but I think the quality of a format is more important than flavor.
Comprehensive overview:
Commons 189 > 192 = +3 (Rescue, unwind, seismic shift)
Uncommon 70 > 64 = -6 (juggernaut, nature's spiral, Orcish vandal, final parting, sage of lat-nam, dauntless bodyguard)
Rare 49 > 48 = -1 (Urza's Ruinous blast)
Mythic 7 > 8 = +1 (Urza's Ruinous blast)
+45 cards
+3 extra boosters
48 Timeshifted cards (cut 3 original DOM)

Now the custom booster draft configuration can be used to draft with proper balance of rarity.