The other issue with the 400 is that good rebuildable cores are getting hard to find. As Coilover said they raced them, a lot of them, and just finding a good clean block is hard. The 383 combination is a proven build, literally thousands have been built, it's also a great motor for building torque. Torque gets you away from the traffic light, horse power gets you to the next one faster.
This place in NE does their own blocks. Does not matter if it is 350 383 or 400. No seasoned cores.
The 383 is 434/450
The 400 is 505/450
Both run similar rpm's. I questioned them about steam passages, rpm range etc. HP and TQ curves are similar, just more with the 400.
