Really when you look at core motors, theres the K which is simple in design push rod single cam, carby yada yada
On the other hand theres the CA, Twincam, EFI, larger capacity =more torque, factory turbo engine (stronger), more refined, more aftermarket support, better choice of turbos, easier custom work.... i could go on but i think you get my point.
If you have 2 70's then go one with a boosted K motor and keep that mildly more legal and then use the CA 70 for the track/occasional street.... that way you have a back up car if one fails due to varying circumstances.
Karl.