I am glad I did not sell off the 2008 Mac Pros. I'd love to get
On Mac Pro 3,1, I use a couple generic Broadcom compatible cards that are listed at "Third-Party Wireless Cards" (have two towers).
Both use a/b/g/n. One allows you to select 2.5 and 5Ghz another does not but has access to what appears to be 5Ghz radios which is strange!. 802.11n over 2.5Ghz actually runs really fast, so I haven't bother finding faster cards. The n radio ones are inexpensive compared to 802.11ac cards for the Mac Pro which cost up to 10 times more.
https://www.amazon.com/gp/product/B010JP3HFK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
There is a trick to popping on the Antenna radios. If you push downward on the out side edge with your index finger then move the rest down like a lever, the cable should pop right on. It took me quite awhile to discover this and if you don't get the cable on right way, you'd be surprised how fast your fingers will get sore over these many attempts. Removing PCIe cards and hard drives can give you more room which I highly recommend doing. You can also use your iPhone's camera along with its torch light to use as a scope to get a good view of what you are doing. I have old eyes, so the iPhone saves me.