How was the end gap on the rings? Were they file fit, or exact fit? Typically around .008"-.010" compression ring endgap is acceptable, but up to .015" will work, but it might use a little oil @ .015".
What kind of bearing clearence do you have? I think on a 350 chevy, you need around .0025 max on the rods, and like .004 max on the mains. I am not sure if the 400’s are the same, as they have different journal sizes.
When you turn it over by hand is it really hard to turn over? Is there any noises that would sound like contact between the valves & pistons?
Do you have a 168 or 153 tooth flywheel? 400 small blocks typically had 168 for better mechanical advantage for the starter. What kind of compression does it have? If you got higher compression & 153 tooth flywheel, you may have issues.