360 block limits

The real limit of what you have isn’t going to be as much the block as it is how much you can control detonation.
9 times out of 10 when a nitrous engine fails, detonation is the culprit. And there’s more to it than just the tune, too such as chamber shape and finish, head gasket selection and using studs to keep the heads and block held tightly together. I think 100hp is doable with a limit of 200, but only if the ring gap is set and you’ve got head studs with premium gaskets that prevent sharp edges at the top of the bore. I’m more in favor of the magnum (or a dedicated nitrous built engine, as CH1ll suggested) for use during the learning curve.