I have a mac pro 3,1 and a mac pro 2,1. My mac pro 3,1 did not have a airport card installed so i took the one out of my 2,1 and it worked fine. The only issue is for some reason it says it only has 802.11 a/b/g support. I have done research and it says it had 802.11 n support as well but mine does not. I think mine may have a old firmware version installed that limits it to a/b/g support but i cant find anywhere to get the updates. Any help would be nice 
. Here are the specs of my mac and the airport card:
AIRPORT:
Card Type: AirPort Extreme (0x14E4, 0x89)
Firmware Version: Broadcom BCM43xx 1.0 (5.10.131.36.16)
MAC Address: 00:14:51:e8:25:07
Locale: FCC
Country Code: US
Supported PHY Modes: 802.11 a/b/g
Supported Channels: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165
Status: Connected
MAC:
Model Name: Mac Pro
Model Identifier: MacPro3,1
Processor Name: Quad-Core Intel Xeon
Processor Speed: 3.2 GHz
Number of Processors: 2
Total Number of Cores: 8
L2 Cache (per Processor): 12 MB
Memory: 32 GB
Bus Speed: 1.6 GHz
Boot ROM Version: MP31.006C.B05
SMC Version (system): 1.25f4
Serial Number (system): G88293DPXYL
Hardware UUID: AA8136A1-9FB8-509D-96CE-1C3C6051D12B
. Here are the specs of my mac and the airport card:AIRPORT:
Card Type: AirPort Extreme (0x14E4, 0x89)
Firmware Version: Broadcom BCM43xx 1.0 (5.10.131.36.16)
MAC Address: 00:14:51:e8:25:07
Locale: FCC
Country Code: US
Supported PHY Modes: 802.11 a/b/g
Supported Channels: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165
Status: Connected
MAC:
Model Name: Mac Pro
Model Identifier: MacPro3,1
Processor Name: Quad-Core Intel Xeon
Processor Speed: 3.2 GHz
Number of Processors: 2
Total Number of Cores: 8
L2 Cache (per Processor): 12 MB
Memory: 32 GB
Bus Speed: 1.6 GHz
Boot ROM Version: MP31.006C.B05
SMC Version (system): 1.25f4
Serial Number (system): G88293DPXYL
Hardware UUID: AA8136A1-9FB8-509D-96CE-1C3C6051D12B