[DZAUTO]

Ditto, all of the above.
All should be the same and 100% interchangeable, literally. My bet is that the balancer wasn't all the way on. Both 350 and 400 crank snouts and balancer hubs have identical dimensions (or at least all the ones I've ever touched). Example, I have a hi-perf 327 balancer on a 400 crank in my 56 Vette. I wanted the 327 balancer because it is the extra wide version with the fins and is neutral balanced (so that when someone looks at it they don't know the engine is a 400). In order to do this, I had to have the front of the 400 crank internally balanced. Everything went together just fine and the pulleys mated just fine.

 

[DZAUTO]

I started to mention that, but then decided not to, because I figured you would notice if it wasn't. If the crank timing gear wasn't on all the way, the timing chain would be slightly crooked and I felt that you would notice that.