Is the 400 a less popular choice only because it's less common than the 350?
Looks like I'm picking up a rebuildable core to replace my tired 305.
Any input is welcome.
Thanks!

The mains are different, so they use a different crank.
The biggest reason is that people used to think they were more prone to overheating. It was actually because people would install heads from 350s and not drill the steam holes.
If you are getting a good core then go for it.

The 400s are great for tons of torque in a small block package. If you can get one get one that is a 509 casting and 2 bolt mains.

Also watch to cause there known for thin cylinder walls and to many over heats can cause it to crack.But other than that i agree they are good for building 406's out of.Pretty stout if done right.Good luck with it if you have one.

I think less common is part of it as well. They only made 400's for a handfull of years, and not in all models.
350's they just kept cranking out untill they switched everything over to the new LS engines...

10 years(1970-1980) 2 and 4 bolt mains 70-73 2 bolt only 74-80

Make sure the steam holes are drilled.

have fun Im jealous.