SSIS 2005 using .NET 4.0 components

I have a set of SSIS packages written in the 2005 environment. Currently, though I have heard this shouldn't work, these packages reference some custom .NET 3.5 assemblies, and they work fine

For reasons I won't go into here, those assemblies must be upgraded to .NET 4.0. Should the old SSIS packages from 2005 work with references to .NET 4.0 assemblies?

Thanks,

Jeff