Now is the best time for that since the introduction of Polymer80 80% lowers. Seriously. You can make a mint and keep your mags. I sold my complete Gen4 17 upper for $389+shipping on eBay and sold my complete lower for $175+shipping via FFL on AR15.com. I couldn't even get a sniff on that gun at $450 complete. I also kept the three 17rd mags...
I see dudes on here struggling to sell 19's and 26's for dumb low prices when they could be parting them out for waaaaaaaaaaaaaaay more. Go check out some SOLD listings on ebay at what complete slide and even stripped slides are selling for. It's unreal. Also, Polymer80 has a 26/27 sized frame coming soon so dudes will be screaming to get some Glock 26 slides. Watch.