(I don't know anything about exhausts ) Would a dual exhaust without a crossover hurt performance on a stock engine? The crossover is there to even out the exhaust pulses from each bank, right?
Yes, you are right. It also has a better sound. You can have an X or an H pipe, bowever, you can run true duals with no crossover, it wont make THAT much of a difference.
My previous owner put an exhaust system on my 66...made it out of plumbing pipe...no cross over, bottle necked/dented reducers, and flowmasters...still sounded good though.
Most exhaust shops can make you an Hpipe or add a cross over for less than $50!
The cross over pipes do have a different sound. I do not use one but only because mine are off and on a lot and it is a pain to take the entire system out rather than one side at a time.
The crossover will "act" as somewhat of a safety loop if you do not use one.
If you have a performance set up and not running a safety loop please consider adding one SOON. A driveshaft failure at speed can be a very ugly situation.