My brother bought an sr15 mod 1 a month ago and a grip pod to go with it. After looking at the bottom of the float tube, there are not any pic rails and none came with the gun. I have seen where you can get the 3in pic rails but there does not seem to be any holes that are threaded on the bottom. Question is, can I still put one of the 3in rails on there? Do you have to thread some of the holes yourself? Don't want him to have to send the grip pod back. Thanks again, RG