Just made a straight up trade for a NIB TAC 15 (or so I thought) Did it over the internet so sight unseen. Instead of a TAC 15 the guy had a 15i. I already had a RRA lower and Magpul PRS and was set to order a Timney trigger. Before I send it back (unopened) is the 15i customizable? Can I substitute my lower and stock for the 15i's set up? I guess what I want to know is, Is the 15i simply a TAC 15 with a separate lower that can't be converted to a firearm? Second, I've seen youtube videos of TAC 15/15i with the biscuit removed and replaced with a drop away rest. Are there any that are commercially available? If not, how do you go about rigging a drop away rest and which one do you start with? Thanks in advance, I've learned a ton about the TAC 15/15i from this forum already.