1) The pigtail specified is WRONG. The instructable points to an IPEX MHF1 to SMA pigtail on Amazon, which you should NOT use. I don't know how the author got it working, but the AC8260 card does NOT fit an MHF1, but MHF4 such as this one here: http://www.ebay.com.au/itm/2x-IPEX-MHF4-to-RP-SMA-Antenna-Pigtail-for-NGFF-M-2-WIFI-WLAN-3G-4G-Modul... 2x IPEX MHF4 to RP-SMA Antenna Pigtail for NGFF M.2 WIFI WLAN 3G 4G Modules | eBay. The two are not compatible, and MHF1 will not fit on the plug (ask me how I know that!).
I'm really sick of this kind of lack of documentation. You should give a proper engineering specifications, not an Amazon link.. To find this out, I had to dig through a multitude of what looks like sales sheets to find out that there is an AC8260 card on the compute board. Even then, AC8260 doesn't come with datasheet, so I found an eBay listing that supplies AC8260 with MHF4 plugs. All because there's no proper documentation..
2) This is subjective, but the design is potentially dangerous. The spot where the Instructable author puts his antennae is very close to the two props. So, if the antenna folds due to, e.g., a harsh landing, either the antenna or the props will shred to pieces, especially in the orientation shown in the photo. As such, I decided to drill a couple of 6.5mm holes through the support plate for the patch antennae. By orienting the antenna so that the folding direction points into the compute board, I can prevent the shredding situation. It looks like the photo below. I personally think it looks better too.