I do not think birthing is an option if you are long arming these quilts. You would have issues with tucks and puckers. If the points will be facing out, then I think a facing is your only option. in this case you need to be sure to leave about .5 inch unquilted from the prairie points seam line so you have space to turn under the raw edge of the backing. You would then hand sew from the back or machine sew from the front close to the prairie point seam. Might want to check with your customers to make sure they understand that it will be machine sewn as they might be expecting hand sewn.