Quick question, given that the 500 1.4 and the panda 100hp are pretty much the same car, would aftermarket exhaust for the 500 fit the 100hp?

very common asked question mate.
here's the link that will explain how to/what u need to install 500 Abarth dual exhaust on panda.
http://www.torqueitalia.net/forum/threads/2950-Fitting-Abarth-500-Exhaust-to-Fiat-Panda-100hp.

Hope this helps

I DONT mean the abarth, just the standard 1.4 16valve, every thing i have read says they are so similar and there are allot more after market options for the 500 compared to the Panda.

Like that thread I linked said. It will not be in the same position and you'll have to other re-welded or cut bumper to one side. Other that than it should be same fit. Just the bumper outlet position is not gonna mach with pandas.