The SBC 350 is (was) the most popular engine in the world for good reason. That popularity has given us zillions of aftermarket parts. The parts and technology have become better and cheaper over time too. It only makes sense to stick with what works.
From there you can add a 400 crank to your 350 and make a 383 stroker and have all the benefits of more cubic inches and a better rod to stroke ratio (long rod engines are better).
400's have their quirks. The smaller displacements seem like a waste of time to me (the power is not there and the aftermarket parts are not there).