Isky 264 Mega in a 400

Yes. I can get 93 octane on any gas station where I live. I'll have to be careful with the timing curve, but I think it's doable. I just wish all these old iron heads had a quench pad like the small block chebys, i'd push the compression up a hair.
You could retard it a couple of degrees from the recommended intake centerline. To close the intake a little later.