Maybe SF will want a replacement (Murphy sliding, maybe?) for Armstead and be willing to swap their 31st pick. They have three 4th round selections so they may be willing to deal.
If you really wanted to dial it in to the gnats ***, looks like the following math works out even.
Cowboys swap firsts with the 49ers. Cowboys get SF's 3rd round selection and their 5th in exchange for our 6th.
That give us picks 31(rd.1), 56(rd. 2) , 87(rd.3), 94(rd.3), 174(rd.5), 176(rd.5), 233(rd.7), and 244(rd.7). I'd take something like that unless something special falls in our lap.