So the 70 teams would be a super league...meaning who-is-in-what-conference technically wouldn't matter. That being said, I think the big-boy conferences would simply want their original 10 members. 7 x 10, basically.
It works out pretty well for 6 groups:
Original (1970s-2000s) PAC-10
Original SEC
Original Big Ten
SWC light, plus OU/OKST (Texas schools + OK schools + Ark)
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After those, you're left with a smattering of schools across the west and plains, plus a bunch of eastern/southeastern schools.
Instead of picking and choosing and making a mess of things in the east, just draw a Mason-Dixon line along the VA/NC border.
There's 10 unaffiliated schools below it (FSU, GT, UCF, Miami, USCe, Clemson, WF, UNC, Duke, NCST) and there's 10 above it (WV, VT, UVa, UMd, Pitt, PSU, RU, BC, Syr + ND instead of Cinci). We finally get our Eastern conference and a southernesque ACC.
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That leaves "the others." 10 schools that aren't naturally in the previous groups.
Utah, BYU....CU....KU, KSU.....UNL...ISU...Mizzou.....Louisville....Cinc innati
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I don't think this works without having a group like this, as there's just not as many programs out west as there are in the east. It's odd having a program like Nebraska in 'the others,' but I'm not sure what else would feasibly occur. Maybe you take the OK schools out of the SWC and throw the Utah schools into it. At least then "the others" would look like an evolved Big 8. Idk.