I am in the process of swapping my 305 for a rebuilt 350 and was wondering which type of valve covers (short or tall) I should purchase. Any information will be helpful!

 

It should not be short or tall, but perimeter or center bolt for the heads on the 350.

 

But in the aftermarket world, you can get either short or tall covers as well.
Go with the short. You don't need tall covers unless you need more under-cover clearance for roller rockers.
And tall covers can cause clearance problems for you with accessories like the alternator, etc.