Thanks Paul, yeah I was hoping they would fit together but the WIFI board sits a good 3 or 4 mm over towards the RJ45 socket which stops anything from going in.
I did manage to cut away from of the RJ45 connector socket which helped a little.
However did come across the following.
https://community.openenergymonitor.org/t/using-the-emontx-v3-with-the-esp8266-huzzah-wifi-module/795
Which says that you can maybe request a ribbon cable. So when I bought my RJ45 brake out box for extra sensors I requested one and the kind people sent me one.
Not tested yet but should make changing these out a lot easer.
great service 
I know its been stated in other places but I think an option long term for emonTx would be an option for a built in WIFI module instead of the battery pack and RF Module.
Thanks,
Richard.