I've posted a Mock config for both endpoints (A and B ) which you can use if you like.
Its a simple mpls setup. (all of the details are in the .rsc files - plain text, use notepad to view and /or make changes)
Simply upgrade both sxt's to 5.21, perform a reset-configuration,afterwards remove configuration and upload the respective files. (UnitACompact and UnitBCompact) from the console type import file-name= " " and thats it, just aim and plug in the lan cables. Both Lan interface does not have an ip address so use the mac-connect feature in winbox to administer/make changes.
WDS functionality would achieve the same effect... its a matter of preference, although a mpls/vpls enabled setup does offer many advantages.
The only caveat would be to adjust nv2 settings accordingly to suit your voip needs (the posted config should be fine though). If your not happy you could always switch to nstreme with a framer policy of none and a framer limit of 1900. This usually works well for me.
Lastly turn down your power as necessary so that the rssi on both ends are in the mid 50's area.
Thats about it. Hope it helps.